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Estella Lynch
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1 UNIT - II

2 Topics to be covered Arrays Strings Packages Java-Doc comments Inheritance Class hierarchy Polymorphism Dynamic Binding final keyword abstract classes

3 Arrays

4 Arrays: An array is a collection of similar type of elements that have contiguous memory locations. An array is a type of variable that can store multiple values. An element on an array is accessed by its index which is non-negative integer. Array is collection of homogenous Data items. Array is classified into three types. 1. One Dimensional Array 2. Two Dimensional Array 3. Multi Dimensional Array Creating an Array 1. Declaring the array 2. Creating memory locations 3. Putting values into the memory locations. 1. Declaration of Array Syntax: data_type arrayname[ ]; Example: int number[ ]; float [ ] marks;

5 2. Creating memory locations Syntax: Examples: arrayname = new data_type [size]; number = new int [5]; average = new float [10]; 3. Declaration and Creation in one step Syntax: Example: 4. Initialization of Arrays data_type arrayname [ ] = new data_type [size]; int number [ ] = new int [5]; Array initializer is a list of comma- seperated expressions surrounded by curly braces. Array will automatically be created large enough to hold the number of elements you specify in the array initializer. For this no need to use new operator. Syntax: Examples: data_type arrayname [ ] = list of values; int number [ ] = 10, 20,30, 40,50; int number[ ] = new int [3] 10,20,30;

6 One Dimensional Array: A list of like-typed elements. First create an array variable of the desired type. new is a special operator that allocates memory. Assigning values are based on the array variable index ranges from 0 to n-1 The values displayed in the output is also based on index. Example 1: class Arrays public static void main(string args[]) int month_days[]; month_days = new int[12]; month_days[0] = 31; month_days[6] = 31; month_days[1] = 28; month_days[7] = 31; month_days[2] = 31; month_days[8] = 30; month_days[3] = 30; month_days[9] = 31; month_days[4] = 31; month_days[10] = 30; month_days[5] = 30; month_days[11] = 31; System.out.println( April has + month_days[3] + days ); O/P: April has 30 days

7 Example 2: class SampleArray public static void main(string args[]) int a[] = new int[10]; System.out.println("Storing the numbers in array"); a[0] = 1; a[1] = 2; a[2] = 3; a[3] = 4; a[4] = 5; a[5] = 6; a[6] = 7; a[7] = 8; a[8] = 9; a[9] = 10; System.out.println("The element at a[5] is : " +a[5]); O/P : Storing the numbers in array The element at a[5] is : 6

8 Example 3: class ArrayFirst1 public static void main(string[] args) int a[] = new int[5]; a[0] = 2; a[1] = 4; a[2] = 6; a[3] = 8; a[4] = 10; for(int i=0;i<=4;i++) System.out.println(a[i]); O/P : Example 4: class ArrayFirst2 public static void main(string[] args) int a[] = new int[5]; a[0] = 2; a[1] = 4; a[2] = 6; a[3] = 8; a[4] = 10; for(int i=0;i<a.length;i++) System.out.println(a[i]); O/P :

9 Example 5: class ArrayFirst3 public static void main(string[] args) int a[] = 10,20,30; for(int i=0;i<3;i++) System.out.println(a[i]); O/P : Example 6: class ArrayFirst4 public static void main(string[] args) O/P : int a[] = 10,20,30; for(int i=0;i<a.length;i++) System.out.println(a[i] + " ");

10 Example 7: class ArraySecond public static void main(string[] args) int a[] = 1,2,3; int b[] = 2,4,6; int c[] = 3,6,9; for(int i=0;i<3;i++) System.out.print(a[i]+ " "); System.out.println(); for(int j=0;j<3;j++) System.out.print(b[j]+ " "); System.out.println(); for(int k=0;k<3;k++) System.out.print(c[k]+ " "); O/P :

11 Example 8: class ArraySecond1 public static void main(string[] args) int a[][] = 2,4,6,1,3,5,1,2,3; for(int i=0;i<3;i++) for (int j=0;j<3;j++) System.out.print(a[i][j]+" "); System.out.println(); O/P :

12 Example 9: class ArrayAddition2 public static void main(string[] args) int a[][] = 1,2,3,4,5,6,1,1,1; int b[][] = 2,4,6,1,3,5,0,0,0; int c[][] = new int[3][3]; for(int i=0;i<3;i++) O/P : for(int j=0;j<3;j++) c[i][j]=a[i][j]+b[i][j]; System.out.println(); System.out.print(c[i][j] + " ");

13 Example 10: class ArrayMul1 public static void main(string args[]) int a[][]=1,2,3,4,5,6; int b[][]=2,4,6,1,3,5; int c[][]=new int[2][3]; for(int i=0;i<2;i++) for(int j=0;j<3;j++) c[i][j]=a[i][j]*b[i][j]; System.out.print(c[i][j]+" "); System.out.println(); O/P:

14 Example 11: import java.io.*; class ArrayUsingBufRead public static void main(string[] arg)throws IOException int a[]=new int[5]; BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); int i; for(i=0;i<a.length;i++) a[i]=integer.parseint(br.readline()); System.out.println(); System.out.println("The values in the array are :" ); for(i=0;i<a.length;i++) System.out.println(" "+a[i]); O/P : The values in the array are :

15 Example 12: class NumberSorting public static void main(string args[]) int number[] = 70,20,10,30,10; int n = number.length; System.out.println("Given List"); for(int i = 0;i<n;i++) System.out.println(" " + number[i]); System.out.print("\n"); for(int i = 0;i < n; i++) for(int j = 0;j < i; j++) if (number[i] < number [j]) int temp = number[i]; number[i] = number[j]; number[j] = temp; System.out.println("Sorted list:"); for(int i = 0;i < n;i++) System.out.println(" " + number[i]); System.out.println(" "); O/P : Given List Sorted list:

16 Example 13: public class CmdLineArgArray public static void main(string arg[]) O/P : int a[]=new int[arg.length]; for(int i=0; i<(arg.length); i++) a[i]=integer.parseint(arg[i]); for(int i=0; i<arg.length; i++) System.out.println(a[i]); E:\Java Programs\Examples\Array>javac CmdLineArgArray.java E:\Java Programs\Examples\Array>java CmdLineArgArray

17 Example 13: public class CmdLineArgArray public static void main(string arg[]) O/P : int a[]=new int[arg.length]; for(int i=0; i<(arg.length); i++) a[i]=integer.parseint(arg[i]); for(int i=0; i<arg.length; i++) System.out.println(a[i]); E:\Java Programs\Examples\Array>javac CmdLineArgArray.java E:\Java Programs\Examples\Array>java CmdLineArgArray

18 The for-each loop: A powerful looping construct that allows repeating for each element in an array without having to confirm with index values. Syntax: for(variable : collection) statement Ex: int a[] = 10,20,30,40,50; for (int b : a) System.out.println(b); Java.util.Arrays: The java.util.arrays class contains a static factory that allows arrays to be viewed as lists. Following are the important points about Arrays: This class contains various methods for manipulating arrays (such as sorting and searching). The methods in this class throw a NullPointerException if the specified array reference is null. Class declaration public class Arrays extends Object

19 Methods static String tostring(type[] a) static type copyof(type[] a, int length) static type copyofrange(type[] a, int start, int end) static void sort(type[] a) static int binarysearch(type[] a, type v) static int binarysearch(type[] a, int start, int end,type v) static void fill(type[] a, type v) static boolean equals(type[] a, type[] b) Usage Returns a string with the elements of a Returns an array of the same type as a, of length, filled with the values of a Returns an array of the same type as a, of length end-start, filled with the values of a Sorts the array Uses the binary search algorithm to search for the value v. If it is found, its index is returned. Otherwise, a negative value r is returned Sets all elements of the array to v Returns true if the arrays have the same length, and if the elements in the corresponding indexes match

20 import java.util.*; Class SDArray public static void main(string args[]) int a[] = new int[5]; int b[] = 4,2,1,6,3; System.out.println( Array Elements in B Before Sorting ); for (int i:b) System.out.println(i); Arrays.sort(b); System.out.println( Array Elements in B After Sorting ); for(int i:b) System.out.println(i); Arrays.fill(a,1); System.out.println( Filled Array Elements in A ); for(int i:a) System.out.println(i); boolean flag = Arrays.equals(a,b); System.out.println( After Checking two Array Elements: + flags); int index = Arrays.binarySearch(b,3); System.out.println( Searched Element Index in B is: +index); System.out.println( Copied Array );

21 Output: a = Arrays.copyOf(b,4); for(int i:b) System.out.println(i); Array Elements in B Before Sorting: Array Elements in B After Sorting: Filled Array Elements in A: After checking two Arrays: false Searched Index element in array B is : 2 Copied Array:

22 Case: It is possible to assign an array object to another. Ex: int [ ] a = 1,2,3; int [ ] b; b = a; Two Dimensional Array Declaration for the Two Dimensional Array int [ ][ ] myarray; myarray = new int[3,3]; OR int [ ][ ] myarray = new int[3,3]; OR int[ ][ ] table = 0,0,0,1,1,1;

23 class MultiTable final static int ROWS = 5; final static int COLUMNS = 5; public static void main(string args[]) int product[][] = new int[rows][columns]; int row,column; System.out.println("Multiplication Table"); System.out.println(" "); int i,j; for(i=1;i<rows;i++) for(j=1;j<columns;j++) product[i][j] = i * j; System.out.print(" " + product[i][j]); System.out.println(" ");

24 Variable Size Arrays Variable Size array is called Array of Array or Nested Array or Jagged Array Ex: int [ ] [ ] x = new int [3] [ ]; //Three rows array x [0] = new int [2] x [1] = new int [4] x [2] = new int [3] //First Rows has two elements //Second Rows has four elements //Third Rows has three elements x[0] x[1] x[0] [1] x[1] [3] x[2] x[2] [2]

25 public class MyArrayc2 public static void main(string args[ ]) throws IOException BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); int [ ][ ]arr=new int[4][ ]; arr[0]=new int[3]; arr[1]=new int[2]; arr[2]=new int[5]; arr[3]=new int[4]; System.out.println("Enter the numbers for Jagged Array"); for(int i=0 ; i < arr.length ; i++) for(int x=0 ; x < arr[i].length ; x++) String st= br.readline(); int num=integer.parseint(st); arr[i][x]=num;

26 System.out.println(""); System.out.println("Printing the Elemnts"); for(int i=0 ; i < arr.length ; i++) for(int y=0 ; y < arr[i].length ; y++) System.out.print(arr[i][y]); System.out.print("\0"); System.out.println("");

27 String in Java

28 String: Java s String type called String, is not a Simple Type, nor is it simply an array of characters. Rather String defines an Object. The String type is used to declare string variable. Java Strings are sequences of Unicode Characters. Use an object of type string as an argument to println(); String str = Welcome to JAVA ; System.out.println(str); Implementing strings as built-in objects allows java to provide a full complement of features that make string handling convenient. Java has methods to compare two strings, search for a substring, concatenate two strings, and change the case of letters within a String. String object has been created, you cannot change the characters that comprise that string. String Constructors: The String class supports several constructors. To create an empty string call the default constructor. String str = new String(); Initialize the values through array of characters. char ch[] = a, b, c ; String str = new String(ch); o/p: abc 1. Subrange: String(char ch[], int start,int numchar); char ch[] = a, b, c, d, e,f ; String s = new String(ch,2,3); o/p: cde

29 2. String copy: String(String strobj); char ch[] = J, A, V, A ; String s1 = new String(ch); String s2 = new String(s1); System.out.println(s1); System.out.println(s2); O/P: JAVA O/P: JAVA 3. ASCII char: String (byte asciichars[]); String(byte asciichars[], int start, int numchars); byte ascii[] =65,66,67,68,69,70; String s1 = new String(ascii); System.out.println(s1); String s2 = new String(ascii,2,3); System.out.println(s2); O/P: ABCDEF O/P: CDE

30 SPECIAL STRING OPERATIONS 1. Automatic creation of new String instances from string literals. 2. Concatenation of multiple String object by used of the + operators 3. Conversion of other data types to a string representation. 1. String Literals To find the length of a String Assigning values to the object. Syntax: String obj = value; class Str_Length public static void main(string args[]) char chars [ ] = 'a', 'b', 'c'; String s1 = new String(chars); String s2 = "Chettinad"; //Use String Literals, Java automatically //constructs a String object System.out.println("The Displayed String_1 is:" + s1); System.out.println("The Displayed String_2 is:" + s2); System.out.println(" The Length of the String is: " + " Chettinad ".length()); System.out.println(" The Length of the String is: " + s2.length());

31 Output E:\Programs\javapgm\RUN>javac Str_Length.java E:\Programs\javapgm\RUN>java Str_Length The Displayed String_1 is:abc The Displayed String_2 is:chettinad The Length of the String is: 11 The Length of the String is: 9

32 2. String in Reverse direction class Str_Reverse public static void main(string args[]) char str[] = 'C','H','E','T','T','I','N','A','D'; String S = new String(str); System.out.println("The String S is " +S); for(int i=s.length()-1;i>=0;i--) System.out.print(str[i]); Output E:\Programs\javapgm\RUN>javac Str_Reverse.java E:\Programs\javapgm\RUN>java Str_Reverse The String S is CHETTINAD DANITTEHC

33 3. String Concatenation class String_Concat public static void main(string args[]) String age = " 9 "; String s = "He is" + age + "Years old."; System.out.println(s); Output E:\Programs\javapgm\RUN>javac String_Concat.java E:\Programs\javapgm\RUN>java String_Concat He is 9 Years old. class String_Concat1 public static void main(string args[]) String str = new String(" Welcome to "); String str1 = new String(" III IT "); System.out.println(str.concat(str1)); Output E:\Programs\javapgm\RUN>javac String_Concat1.java E:\Programs\javapgm\RUN>java String_Concat1 Welcome to III IT

34 String Concatenation with Other Data Types class String_Concat2 public static void main(string args[]) int age = 9; String s1 = "He is " + age + " Years old. "; System.out.println(s1); String s2 = "four: " ; System.out.println(s2); String s3 = "four: " + (2 + 2); System.out.println(s3); Output E:\Programs\javapgm\RUN>javac String_Concat2.java E:\Programs\javapgm\RUN>java String_Concat2 He is 9 Years old. four: 22 four: 4

35 4. String Conversion and tostring() To implement tostring(), simply return a String object that contains the human readable string. class Box double width; double height; double depth; Box(double w,double h,double d) width = w; height = h; depth = d; public String tostring() return "Dimensions are " + width + " by " + depth + " by " + height + ".";

36 class String_Operation public static void main(string args[]) Box b = new Box(10, 12, 14); String s = "Box b: " + b; // Concatenate Box object System.out.println(b); System.out.println(s);

37 CHARACTER EXTRACTION The String class provides a number of ways in which characters can be extracted form a String object. That is Character Extraction. 1. charat() Syntax: char charat(int where) class Char_At public static void main(string args[ ]) char ch; ch = "Chettinad".charAt(6); System.out.println("The 6th Character is:" + ch); Output E:\Programs\javapgm\RUN>javac Char_At.java E:\Programs\javapgm\RUN>java Char_At The 6th Character is:n

38 2. getchars() getchars() method. If you need to extract more than one character at a time, you can use the Syntax: void getchars(int sourcestart,int sourceend,char target [ ],int targetstart) class Get_Chars public static void main(string args[]) String s = "This is a demo of the getchars method."; int start = 10; int end = 14; char buf [ ] = new char[end - start]; s.getchars(start,end,buf,0); System.out.println(buf); Output E:\Programs\javapgm\RUN>javac Get_Chars.java E:\Programs\javapgm\RUN>java Get_Chars demo

39 3. tochararray() If you want to convert all the characters in a String object into a character array, the easiest way is to call tochararray(). It returns an array of characters for the entire string. It has this general form: char [ ] tochararray() class Str_ToCharArray public static void main(string args[]) String str = "einstein relativity concept is still a concept of great discussion"; char ch[ ] = str.tochararray(); System.out.println("Converted value from String to char array is: "); System.out.println(ch); Output E:\Programs\javapgm\RUN>javac Str_ToCharArray.java E:\Programs\javapgm\RUN>java Str_ToCharArray Converted value from String to char array is: einstein relativity concept is still a concept of great discussion

40 STRING COMPARISON 1. equals() and equalsignorecase() To compare two strings for equality, use equals() Syntax: boolean equals(string str) Here, str is the String object being compared with the invoking String object. It returns true if the strings contain the same characters in the same order, and false otherwise. The comparison is case - sensitive. To perform a comparison that ignores case differences, call equalsignorecase(). When it compares two string, it considers A - Z to be the same as a - z. Syntax: boolean equalsignorecase(string str) Here, str is the String object being compared with the invoking String object. It, too, returns true if the strings contain the same characters in the same order, and false otherwise.

41 Example - equals class StrEquals public static void main (String args[]) String s1 = new String("WELCOME"); String s2 = new String("welcome"); //if(s1.equals(s2) == true) if(s1.equalsignorecase(s2) == true) System.out.println("\n The two strings are equal"); else System.out.println("\n The two strings are not equal"); Output E:\Programs\javapgm\RUN>javac StrEquals.java E:\Programs\javapgm\RUN>java StrEquals The two strings are equal

42 Example equalsignorecase class StrEquals1 public static void main(string args[]) String s1 = "Hello"; String s2 = "Hello"; String s3 = "Good - Bye"; String s4 = "HELLO"; System.out.println(s1 + " equals " + s2 + " -> " + s1.equals(s2)); System.out.println(s1 + " equals " + s3 + " -> " + s1.equals(s3)); System.out.println(s1 + " equals " + s4 + " -> " + s1.equals(s4)); System.out.println(s1 + " equalsignorecase " + s4 + " -> " + s1.equalsignorecase(s4)); Output E:\Programs\javapgm\RUN>javac StrEquals1.java E:\Programs\javapgm\RUN>java StrEquals1 Hello equals Hello -> true Hello equals Good - Bye -> false Hello equals HELLO -> false Hello equalsignorecase HELLO -> true

43 2. regionmatches() The regionmatches() method compares a specific region inside a string with another specific region in another string. There is an overloaded form that allows you to ignore case in such comparisons. Syntax: boolean regionmatches(int str1startindex, String str2, int str2startindex, int numchars) boolean regionmatches(boolean ignorcase, int str1startindex, String int str2startindex, int numchars) str2,

44 class String_Operation public static void main(string args[]) String str1 = new String("Java is a wonderful language"); String str2 = new String("It is an object-oriented language"); boolean result = str1.regionmatches(20, str2, 25, 8); System.out.println(result); Output: true class String_Operation public static void main(string args[]) String str1 = new String("Java is a wonderful language"); String str2 = new String("It is an object-oriented Language"); boolean result = str1.regionmatches(true, 20, str2, 25, 8); System.out.println(result); Output : true

45 2. startswith() and endswith() string. The startswith() method determines whether a given String begins with a specified The endswith() method determines whether the String in questions ends with a specified string. Syntax: boolean startswith(string str) boolean endswith(string str) str is the String object being tested. If the string matches, true is returned. Otherwise false is returned

46 class Str_Start_End public static void main(string args[]) boolean a, b; a = "Chettinad".startsWith("Chi"); b = "Chettinad".endsWith("nad"); System.out.println("The Start of the String is: " + a); System.out.println("The End of the String is:" + b); Output E:\Programs\javapgm\RUN>javac Str_Start_End.java E:\Programs\javapgm\RUN>java Str_Start_End The Start of the String is: false The End of the String is:true

47 3. equals() Versus == The equals function and == operator are perform two different operations The equals() method compares the characters inside a String object. The == operator compares two object references to see whether they refer to the same instance. Syntax: obj1.equals(obj2); (obj1 == obj2); return type is Boolean. class StrEquals2 public static void main(string args[]) String s1 = "Hello1234"; String s2 = new String(s1); System.out.println(s1 + " equals " + s2 + " -> " + s1.equals(s2)); System.out.println(s1 + " == " + s2 + " -> " + (s1 == s2)); Output E:\Programs\javapgm\RUN>javac StrEquals2.java E:\Programs\javapgm\RUN>java StrEquals2 Hello1234 equals Hello1234 -> true Hello1234 == Hello1234 -> false

48 4. compareto() Syntax: int compareto(string str); Value Less than zero Greater than zero Zero Meaning The invoking string is less than str. The invoking string greater than str. The two strings are equal.

49 class Str_Compare public static void main(string args[]) String s1 = "Chettinad1"; String s2 = "Chettinad"; int n = s1.compareto(s2); if (n==0) System.out.println("The Two String are Equal"); else if(n>0) System.out.println("The First Strings is Greater than the Second String"); else if(n<0) System.out.println("The First String is Smaller than the Second String"); Output E:\Programs\javapgm\RUN>javac Str_Compare.java E:\Programs\javapgm\RUN>java Str_Compare The Two String are Equal

50 MODIFYING A STRING 1. substring() substring() has two forms. 1. String substring(int startindex) 2. String substring(int startindex,int endindex) class Str_SubString1 public static void main(string args[ ]) String s1 = "This is a test. This is, too."; String s2 = s1.substring(5); String s3 = s1.substring(5,12); System.out.println("The Sub String of S2 is: " + s2); System.out.println("The Sub String of S3 is: " + s3); Output E:\Programs\javapgm\RUN>javac Str_SubString1.java E:\Programs\javapgm\RUN>java Str_SubString1 The Sub String of S2 is: is a test. This is, too. The Sub String of S3 is: is a te

51 2. concat() You can concatenate two strings using concat() Syntax: String concat(string str); class String_Operation public static void main(string args[ ]) String s1 = "One"; String s2 = s1.concat(" Two"); System.out.println("The Concatenation of Two String is: " + s2);

52 3. replace() The replace() method replaces all occurences of one character in the invoking string with another character. Syntax: String replace(char original, char replacement) class Str_Replace public static void main(string args[ ]) String s = "Hello".replace('l','w'); System.out.println("The Replacement of the String is:" + s); Output E:\Programs\javapgm\RUN>javac Str_Replace.java E:\Programs\javapgm\RUN>java Str_Replace The Replacement of the String is:hewwo

53 4. trim() The trim() method returns a copy of the invoking string from which any leading and trailing whitespace has been removed. Syntax: String trim() class Str_Trim public static void main(string args[ ]) String s = " Hello world".trim(); System.out.println("The Removable Whitespace of the String is: " + s); Output E:\Programs\javapgm\RUN>javac Str_Trim.java E:\Programs\javapgm\RUN>java Str_Trim The Removable Whitespace of the String is:hello world

54 5. touppercase() and tolowercase() class Str_Upper_Lower public static void main(string args[]) String str = new String("Welcome to III IT"); System.out.println("\n The Original String is: " +str); String str_upper = str.touppercase(); System.out.println("The Upper Case String is: " +str_upper); String str_lower = str.tolowercase(); System.out.println("The Lower Case String is: " +str_lower); Output E:\Programs\javapgm\RUN>javac Str_Upper_Lower.java E:\Programs\javapgm\RUN>java Str_Upper_Lower The Original String is: Welcome to III IT The Upper Case String is: WELCOME TO III IT The Lower Case String is: welcome to iii it

55 StringBuffer Functions 1. StringBuffer is a peer class of String that provides much of the functionality of strings. 2. String Buffer represents growable and writeable character sequences. 3. String Buffer may have characters and substrings inserted in the middle or appended to the end. 4. String Buffer will automatically grow to make room for such additions and often has more characters preallocated than are actually needed, to allow room for growth. StringBuffer Constructors StringBuffer defined these three constructors: 1. StringBuffer() - The default constructor reserves room for 16 characters without reallocation. 2. StringBuffer(int size) - The second version accepts an integer argument that explicitly sets the size of the buffer. 3. StringBuffer(String str) - The third version accepts a String argument that sets the initial contents of the StringBuffer object and reserves room for 16 more characters without reallocation.

56 1. length() and capacity() Syntax: int length() int capacity() class Str_Length_Capacity public static void main(string args[ ]) StringBuffer sb = new StringBuffer("Hello"); System.out.println("Buffer = " + sb); System.out.println("Length = " + sb.length()); System.out.println("Capacity = " + sb.capacity()); //Its capacity is 21 //because room for 16 additional characters is automatically added. Output E:\Programs\javapgm\RUN>javac Str_Length_Capacity.java E:\Programs\javapgm\RUN>java Str_Length_Capacity Buffer = Hello Length = 5 Capacity = 21

57 2. setlength() Syntax: To set the length of the buffer within a StringBuffer object, use setlength(). void setlength(int len) Here, len specifies the length of the buffer. This value must be non - negative. when you increase the size of the buffer, null characters are added to the end of the existing buffer. class Str_SBSetLength public static void main(string[ ] args) // Construct a StringBuffer object: StringBuffer s = new StringBuffer("Hello world!"); s.setlength(7); // Change the length of buffer to 7 characters: System.out.println(s); Output E:\Programs\javapgm\RUN>javac Str_SBSetLength.java E:\Programs\javapgm\RUN>java Str_SBSetLength Hello w

58 3. charat() and setcharat() 1. The value of a single character can be obtained from a StringBuffer via the charat() method. Syntax: char charat(int where) For charat(), where specifies the index of the character being obtained. 2. You can set the value of a character within a StringBuffer using setcharat(). Syntax: void setcharat(int where,char ch) For setcharat(), where specifies the index of the character being set, and ch specifies the new value of that character. For both methods, where must be nonnegative and must not specify a location beyond the end of the buffer.

59 class Str_SetCharAt1 public static void main(string args[]) StringBuffer sb = new StringBuffer("Hello"); System.out.println("Buffer before = " + sb); System.out.println("charAt (1) before = " + sb.charat(1)); sb.setcharat(1,'i'); sb.setlength(2); System.out.println("Buffer after = " + sb); System.out.println("charAt(1) after = " + sb.charat(1)); Output E:\Programs\javapgm\RUN>javac Str_SetCharAt1.java E:\Programs\javapgm\RUN>java Str_SetCharAt1 Buffer before = Hello charat (1) before = e Buffer after = Hi charat(1) after = i

60 class Str_SetCharAt2 public static void main(string args[]) StringBuffer sb = new StringBuffer("Great"); System.out.println("The String is: " + sb); sb.setcharat(1,'o'); sb.setcharat(2,'d'); sb.setlength(3); System.out.println("Now the String is: " +sb); Output E:\Programs\javapgm\RUN>javac Str_SetCharAt2.java E:\Programs\javapgm\RUN>java Str_SetCharAt2 The String is: Great Now the String is: God

61 4. append() 1. The append() method concatenates the string representation of any other type of data to the end of the invoking StringBuffer object. 2. It has overloaded versions for all the built - in types and for Object. 3. Here are a few of its forms: StringBuffer append(string str) StringBuffer append(int num) StringBuffer append(object obj) 4. String.valueOf() is called for each parameter to obtain its string representation. 5. The result is appended to the current StringBuffer object. The buffer itself is returned by each version of append().

62 StringBuffer append(string str) public class Str_Append1 public static void main(string[] args) // Construct a String object: String s1 = new String("3.14"); // Construct a StringBuffer object: StringBuffer s = new StringBuffer("The ratio is: "); // Append the string and display the buffer: System.out.println(s.append(s1) + "."); Output E:\Programs\javapgm\RUN>javac Str_Append1.java E:\Programs\javapgm\RUN>java Str_Append1 The ratio is: 3.14.

63 StringBuffer append(int num) class Str_Append2 public static void main(string args[]) String s; int a = 42; StringBuffer sb = new StringBuffer(); s = sb.append("a = ").append(a).append("!").tostring(); System.out.println(s); Output E:\Programs\javapgm\RUN>javac Str_Append2.java E:\Programs\javapgm\RUN>java Str_Append2 a = 42!

64 StringBuffer append(object obj) class Str_Append3 public static void main(string[] args) // Declare and initialize an object: Object d = new Double(3.14); // Construct a StringBuffer object: StringBuffer s = new StringBuffer("The ratio is: "); Output // Append the object and display the buffer: System.out.println(s.append(d) + "."); E:\Programs\javapgm\RUN>javac Str_Append3.java E:\Programs\javapgm\RUN>java Str_Append3 The ratio is: 3.14.

65 5. insert() 1. The insert() method inserts one string into another. 2. It is overloaded to accept values of all the simple types, plus Strings and Objects. 3. Like append(), it calls String.valueOf() to obtain the string representation of the value it is called with. 4. These are a few of its forms: StringBuffer insert(int index,string str) StringBuffer insert(int index,char ch) StringBuffer insert(int index, object obj) Here, index specifies the index at which point the string will be inserted into the invoking StringBuffer object.

66 StringBuffer insert(int index,string str) class Str_Insert1 public static void main(string[] args) // Construct a StringBuffer object: StringBuffer buf = new StringBuffer("Hello!"); String s = new String("there"); // Construct a String object: buf = buf.insert(6,s); // Insert the string "s" at offset 6: Output System.out.println(buf); // Display the buffer: E:\Programs\javapgm\RUN>javac Str_Insert1.java E:\Programs\javapgm\RUN>java Str_Insert1 Hello there!

67 StringBuffer insert(int index,string str) class Str_Insert4 public static void main(string[] args) StringBuffer str = new StringBuffer(" in need is a in deed"); StringBuffer new_str = new StringBuffer(" FRIEND"); System.out.println("Initially the String is: "+str); str.insert(13,new_str); str.insert(0,new_str); System.out.println("Now the String is: " +str); Output E:\Programs\javapgm\RUN>javac Str_Insert4.java E:\Programs\javapgm\RUN>java Str_Insert4 Initially the String is: in need is a in deed Now the String is: FRIEND in need is a FRIEND in deed

68 StringBuffer insert(int index,char ch) public class Str_Insert2 public static void main(string[] args) // Construct a StringBuffer object: StringBuffer buf = new StringBuffer("Hello #!"); // Insert 'J' at the offset 6: buf = buf.insert(6,'j'); // Display the buffer: System.out.println(buf); Output E:\Programs\javapgm\RUN>javac Str_Insert2.java E:\Programs\javapgm\RUN>java Str_Insert2 HelloJ #!

69 StringBuffer insert(int index, object obj) class Str_Insert3 public static void main(string[] args) // Construct a StringBuffer object: StringBuffer buf = new StringBuffer("Hello!"); Object d = new Double(3.45); // Construct an object: buf = buf.insert(6,d); // Insert d at the offset 6: System.out.println(buf); // Display the buffer: Output E:\Programs\javapgm\RUN>javac Str_Insert3.java E:\Programs\javapgm\RUN>java Str_Insert3 Hello 3.45!

70 6. reverse() Syntax: You can reverse the character within StringBuffer object using reverse(). StringBuffer reverse() class Str_BufReverse public static void main(string args[]) StringBuffer s = new StringBuffer("abcdef"); System.out.println(s); s.reverse(); System.out.println(s); Output E:\Programs\javapgm\RUN>javac Str_BufReverse.java E:\Programs\javapgm\RUN>java Str_BufReverse abcdef fedcba

71 7. delete() and deletecharat() StringBuffer the ability to delete characters using the methods delete() and deletecharat(). Syntax: StringBuffer delete(int startindex, int endindex) StringBuffer deletecharat(int loc) class Str_BufDelete public static void main(string args[]) StringBuffer sb = new StringBuffer("This is a Test."); sb.delete(0,3); System.out.println("After delete: " + sb); sb.deletecharat(3); System.out.println("After deletecharat: " + sb); Output E:\Programs\javapgm\RUN>javac Str_BufDelete.java E:\Programs\javapgm\RUN>java Str_BufDelete After delete: s is a Test. After deletecharat: s i a Test.

72 8. replace() It replace one set of character with another set inside a StringBuffer object. StringBuffer replace(int startindex, int endindex, String str); class Str_BufReplace public static void main(string args[]) StringBuffer sb = new StringBuffer("This is a test."); System.out.println("Original String: " + sb); sb.replace(5,7, "was"); System.out.println("After Replace: " + sb); sb.replace(2,4, "at"); System.out.println("After Replace: " + sb); Output E:\Programs\javapgm\RUN>javac Str_BufReplace.java E:\Programs\javapgm\RUN>java Str_BufReplace Original String: This is a test. After Replace: This was a test. After Replace: That was a test.

73 9. substring() Syntax: String substring(int startindex) String substring(int startindex,int endindex) class Str_BufSubString public static void main(string args[]) StringBuffer sb = new StringBuffer("Chettinad"); System.out.println("The Original string is: " +sb); String s2=sb.substring(6); System.out.println("The Substring is: " +s2); String s3=sb.substring(2,5); System.out.println("The Substring is: " +s3); Output E:\Programs\javapgm\RUN>javac Str_BufSubString.java E:\Programs\javapgm\RUN>java Str_BufSubString The Original string is: Chettinad The Substring is: nad The Substring is: ett

74 PACKAGES

75 What is Packages? A package is a group of similar types of classes, interfaces and sub-packages. The grouping is usually done according to functionality. In fact, packages act as containers for classes. Package can be categorized in two form, built-in package and user-defined package. There are many built-in packages such as java, lang, awt, javax, swing, net, io, util, sql etc. Benefits of Packages 1. The classes contained in the packages can be easily reused. 2. In packages, classes can be unique compared with classes in other packages. That is, two classes in two different packages can have the same name. They may be referred by their fully qualified name, comprising the package name and class name. 3. Package provide a way to hide classes thus preventing other programs or package from accessing classes that are meant for internal use only. 4. Packages also provide a way for separating design from coding. First we can design classes and decide their relationships, and then we can implement the java code needed for the methods. It is possible to change the implementation of any method without affecting the rest of the design.

77 Types of Packages Java packages are therefore classified into two types. 1. Pre defined packages (Java API Packages) 2. User defined packages 1.Java API Packages Package Name java.lang java.util java.io java.awt java.net java.applet Contents Language support classes. These are classes that java compiler itself uses and therefore they are automatically imported. They include classes for primitive types, strings, math functions, threads and exceptions Language utility classes such as date, vectors, hash tables, random numbers, etc. Input / Output support classes. They provide facilities for the input and output of data. Set of classes for implementing graphical user interface. They include classes for windows, buttons, lists, menus and so on. Classes for networking. They include classes for communicating with local computers as well as with internet servers. Classes for creating and implementing applets.

78 2. USER DEFINED PACKAGES How to Create our own Packages Creating our own package involves the following steps: 1. Declare the package at the beginning of a file using the form package package_name; 2. Define the class that is to be put in the package and declare it public 3. Create a subdirectory under the directory where the main source files are stored. 4. Store the listing as the classname.java file in the subdirectory created. 5. Compile the file. This creates.class file in the subdirectory. 6. The subdirectory name must match the package name exactly. Note: Java also supports the concept of package hierarchy. This done by specifying multiple names in a package statement, separated by dots. Example: package firstpackage.secondpackage;

80 Example : package pack; public class mypack public static void main(string args[]) System.out.println( Welcome ); How to compile & run: Z:\Programs\javapgm>javac -d. mypack.java Z:\Programs\javapgm>java pack.mypack Welcome Z:\Programs\javapgm> The d specifies the destination where to put the generated class file. The. (dot) represents the current folder.

81 Example: Create Package: How to import the package: package package1; public class ClassA public void displaya() System.out.println("Class A"); import package1.classa; class PackageTest1 public static void main(string args[]) ClassA objecta = new ClassA() objecta.displaya();

82 How to run: Z:\Programs\javapgm>javac -d z:\programs\javapgm z:\programs\javapgm\classa.java Z:\Programs\javapgm>javac PackageTest1.java Z:\Programs\javapgm>java PackageTest1 Class A

83 Example : PACKAGE: package PackageTest; import java.io.*; public class Book int book_no, book_id, book_pages; public Book(int a, int b, int c) book_no=a; book_id=b; book_pages=c; public void bookinfo() System.out.println( The Book No +book_no); System.out.println( The Book Id +book_id); System.out.println( The Book Pages +book_pages);

84 Example 2: PROGRAM: import java.io.*; import PackageTest.Book; public class BookReader public static void main(string[] args) Book b=new Book(10, 15, 90); b.bookinfo(); How to run: Z:\Programs\javapgm>javac -d z:\programs\javapgm z:\programs\javapgm\book.java (or) Z:\Programs\javapgm>javac d. Book.java Z:\Programs\javapgm>javac BookReader.java Z:\Programs\javapgm>java BookReader The Book No: 12 The Book Id: 15 The Book Pages: 86 Z:\Programs\javapgm>

85 How to Access package from another package 1.import package.*; 2.import package.classname; 3.fully qualified name Using packagename.* If packagename.* is used then all the classes and interfaces of this package will be accessible but not subpackages. A.Java B.Java package mypackb; package packa; import packa.*; public class A class B public void msg() public static void main(string args[]) System.out.println( Welcome ); A obj=new A(); obj.msg();

86 using package.classname; A.Java package packa; public class A public void msg() System.out.println( Chettinad ); B.Java package mypackb; import packa.a; class B public static void main(string args[]) A obj=new A(); obj.msg();

87 Using fully qualified name Only declared class of this package will be accessible A.Java package packa; public class A public void msg() System.out.println( EEE ); B.Java package mypackb; class B public static void main(string args[]) packa.a obj=new packa.a(); //using fully qualified name obj.msg();

88 Example program for the above Access Protection Tabular Protection.java: package p1; public class Protection int n = 1; private int n_pri = 2; protected int n_pro = 3; public int n_pub = 4; public Protection() System.out.println("base constructor"); System.out.println("n = " + n); System.out.println("n_pri = " + n_pri); System.out.println("n_pro = " + n_pro); System.out.println("n_pub = " + n_pub);

89 This is file Derived.java: package p1; public class Derived_Prot extends Protection public Derived() System.out.println("derived constructor"); System.out.println("n = " + n); //System.out.println("n_pri = " + n_pri); //Cannot Access because //accessing level is same class //in same package System.out.println("n_pro = " + n_pro); System.out.println("n_pub = " + n_pub);

90 This is file SamePackage.java: package p1; public class SamePackage public SamePackage() Protection p = new Protection(); System.out.println("same package constructor"); System.out.println("n = " + p.n); //System.out.println("n_pri = " + p.n_pri); //Cannot Access because //accessing level is same //class in same package System.out.println("n_pro = " + p.n_pro); System.out.println("n_pub = " + p.n_pub);

91 This is file OtherPackage.java: package p1.p2; public class Protection2 extends p1.protection public Protection2() System.out.println("derived other package constructor"); // System.out.println("n = " + n); //Cannot Access because //accessing level is non sub //class same class // System.out.println("n_pri = " + n_pri); //Cannot Access because //accessing level is same //class in same package System.out.println("n_pro = " + n_pro); System.out.println("n_pub = " + n_pub);

92 This is file OtherPackage.java: package p1.p2; class OtherPackage OtherPackage() p1.protection p = new p1.protection(); System.out.println("other package constructor"); // System.out.println("n = " + p.n); // Cannot access because the // accessing level is non sub // class in same package // System.out.println("n_pri = " + p.n_pri); // Cannot access // because the accessing // level is same class in // same package // System.out.println("n_pro = " + p.n_pro); // Cannot access // because the accessing // level is sub class in // other package System.out.println("n_pub = " + p.n_pub);

93 JavaDoc Comments

94 JavaDoc Comments: Javadoc is a tool which comes with JDK and it is used for generating Java code documentation in HTML format from Java source code which has required documentation in a predefined format. The Java language supports three types of comments: Types of Comments Class Comments - /*.*/ and /* * */ Method @throws Field Comments Data Members - /* * */ General @since.

95 Single Line Comments Single line comments are used to add a very brief comment within some code, often a long or complex method. They begin with a double forward slash (//) and end with the end of line or carriage return. As an example consider: private static String name = Welcome"; //The name to print Multi Line Comments If a comment is going to span across more than one line then a multi-line comment should be used. These are often useful for providing more in-depth information. It start with a forward slash followed by an asterisk (/*) and end with an asterisk followed by a forward slash (*/). Consider: /* Getter method provides public access in read only fashion. This function returns the port number. */ int getport()...

96 Javadoc Comments Javadoc Comments are specific to the Java language and provide a means for a programmer to fully document his / her source code as well as providing a means to generate an Application Programmer Interface (API) for the code using the javadoc tool that is bundled with the JDK The Format of Javadoc Comments A Javadoc comment precedes any class, interface, method or field declaration and is similar to a multi-line comment except that it starts with a forward slash followed by two atserisks (/**). The basic format is a description followed by any number of predefined tags. Generally paragraphs should be separated or designated with the <p> tag. Java supports the following types of comments. Class level comments which describe the purpose of classes and Member level comments describe the purpose of members.

97 EXAMPLE Class Level Comments author XYZ The Employee class contains salary of each employee */ public class Employee //Employee class code Member Level Comments XYZ */ /** Class Description of MyClass */ public class MyClass /** Field Description of integer value for myintfield */ public int myintfield; /** Constructor Description of MyClass() */ public MyClass() // Do something...

98 Example /** * The HelloWorld program implements an application that * simply displays "Hello World!" to the standard output. * John */ public class HelloWorld public static void main(string[] args) /* Prints Hello, World! on standard output. */ System.out.println("Hello World!");

99 The JavaDoc Tags:

100

101

102

103 General Order of Tags The general order in which the tags occur is

104

Lab 14 & 15: String Handling

Lab 14 & 15: String Handling Prof. Navrati Saxena TA: Rochak Sachan String Handling 9/11/2012 22 String Handling Java implements strings as objects of type String. Once a String object has been created,