OBJECT ORIENTED PROGRAMMING. Course 3 Loredana STANCIU Room B616

Transcription

1 OBJECT ORIENTED PROGRAMMING Course 3 Loredana STANCIU loredana.stanciu@aut.upt.ro Room B616

2 Summary of course 2 Primitive data types Variables, arrays Operators Expressions Statements and blocks Control flow statements Classes and objects

3 The primitive data types Primitive types to define variables: int i = 2; float j; double d;

4 The Numbers classes Wrapper classes for each of the primitive data types Wrap the primitive type in an object Often, the wrapping is done by the compiler The compiler boxes a primitive type in its wrapper class (unboxes the object into a primitive type) Integer x, y; x = 12; y = 15; System.out.println(x+y);

5 Java.lang

6 The Numbers classes All of the numeric wrapper classes are subclasses of the abstract class Number

7 The Numbers classes All of the numeric wrapper classes are subclasses of the abstract class Number

8 The Numbers classes Why to use a Number object rather than a primitive? As an argument of a method that expects an object To use constants defined by the class, such as MIN_VALUE and MAX_VALUE, that provide the upper and lower bounds of the data type. To use class methods for various conversions

9 Methods Implemented by all Subclasses of Number Converts the value of this Number object to the primitive data type returned. byte bytevalue() short shortvalue() int intvalue() long longvalue() float floatvalue() double doublevalue()

10 Methods Implemented by all Subclasses of Number Compares this Number object to the argument. int compareto(byte anotherbyte) int compareto(double anotherdouble) int compareto(float anotherfloat) int compareto(integer anotherinteger) int compareto(long anotherlong) int compareto(short anothershort)

11 Methods Implemented by all Subclasses of Number boolean equals(object obj) Determines whether this number object is equal to the argument. The methods return true if the argument is not null and is an object of the same type and with the same numeric value.

12 Conversion Methods, Integer Class static int parseint(string s) Returns an integer (decimal only). String tostring() Returns a String object representing the value of this Integer. static String tostring(int i) Returns a String object representing the specified integer.

13 Conversion Methods, Integer Class static Integer valueof(int i) Returns an Integer object holding the value of the specified primitive. static Integer valueof(string s) Returns an Integer object holding the value of the specified string representation.

14 Formatting Numeric Print Output The java.io package includes a PrintStream class: the System.out object represents the standard output (the screen) can be used to invoke every printing method described in PrintStream

15 Formatting Numeric Print Output The java.io package includes a PrintStream class System.out.println(String s) System.out.format(String format, Object... args) System.out.printf(String format, Object... args) System.out.format(Locale l, String format, Object... args)

16 Formatting Numeric Print Output The conversion characters Conversion Argument Description category c, C character The result is a Unicode character s string The result is a string d integral The result is formatted as a decimal integer e, E floating point The result is formatted as a decimal number in computerized scientific notation f floating point The result is formatted as a decimal number g, G floating point The result is formatted using computerized scientific notation or decimal format, depending on the precision and the value after rounding n line separator The result is the platform-specific line separator

17 Formatting Numeric Print Output System.out.format("The value of the float variable is %f, " + " the value of the integer " + " variable is %d, and the " + "string is %s", floatvar, intvar, stringvar); matter.html

18 Formatting Numeric Print Output int i = ; System.out.format("The value of i is: %d%n", i); The output: The value of i is: float floatvar = 3.14; System.out.format(Locale.FRANCE, "The value of the float variable is %f%n", floatvar); The output: The value of the float variable is: 3,14

19 Formatting Numeric Print Output To use a Local constant the java.util package should be imported into your program Extra information regarding the subject: s/api/java/util/locale.html

20 Formatting Numeric Print Output long n = ; System.out.format("%d%n", n); System.out.format("%08d%n", n); System.out.format("%+8d%n", n); System.out.format("%,8d%n", n); 461,012 System.out.format("%+,8d%n", n); +461,012

21 Formatting Numeric Print Output double pi = Math.PI; System.out.format("%f%n", pi); System.out.format("%.3f%n", pi); System.out.format("%10.3f%n", pi); System.out.format("%-10.3f%n", pi); System.out.format(Locale.FRANCE, "%- 10.4f%n%n", pi); 3,1416 import java.util.*;

22 Advanced mathematical computation import java.lang.math.*; int abs(float f) int round(float f) int min(int arg1, int arg2) int max(int arg1, int arg2) double exp(double d) double log(double d) double pow(double base, double exponent) double sqrt(double d)

23 Advanced mathematical computation double sin(double d) double cos(double d) double tan(double d) double asin(double d) double acos(double d) double atan(double d) double todegrees(double d) double toradians(double d)

24 Advanced mathematical computation

25 Advanced mathematical computation Random Numbers random() method returns a pseudo-randomly selected number between 0.0 and 1.0 (exclusively) int number = (int)(math.random() * 10); Two defined constants E the base of natural logarithms PI the ratio of the circumference of a circle to its diameter

26 Summary of numbers Wrapper classes Byte, Double, Float, Integer, Long, or Short to wrap a number of primitive type in an object The Number classes include constants and useful class methods To format a string containing numbers for output, you can use the printf() or format() methods in the PrintStream class The Math class contains a variety of class methods for performing mathematical functions

27 Problem Compute the following expression: y 3x 2x 1 The value of x should be randomly generated as a number less than 100. x and y are floating point numbers. Print on the screen, formatted in Romanian style, the values of x and y using 8 digits out of which 2 are used to represent the floating point part

28 Solution import java.util.*; class Solution{ public static void main(string[] arg){ double x = (double)(math.random() * 100); double y = 3*Math.pow(x,2) + 2*x +1; System.out.format(Local.FRANCE, For x = %8.2f,y = %8.2f,x,y); } } Output: For x= 81,59 y= 20136,18

29 Characters char primitive type Character wrapper class The Character class is immutable, so that once it is created, a Character object cannot be changed. Creating an Character object: Character ch = new Character('a'); autoboxing or unboxing Character test(character c) {...} char c = test('x'); java.lang.character

30 Characters Usefull methods boolean isletter(char ch) boolean isdigit(char ch) boolean iswhitespace(char ch) boolean isuppercase(char ch) boolean islowercase(char ch) char touppercase(char ch) char tolowercase(char ch) tostring(char ch)

31 Characters Escape sequences (preceded by a \ ) Escape Description Sequance \t Insert a tab in the text at this point. \b Insert a backspace in the text at this point. \n Insert a newline in the text at this point. \r Insert a carriage return in the text at this point. \f Insert a formfeed in the text at this point. \ Insert a single quote character in the text at this point. \ Insert a double quote character in the text at this point. \\ Insert a backslash character in the text at this point.

32 Characters When do you need an escape sequences? If you want to print the following message: She said "Hello!" to me. You should write System.out.println("She said \"Hello!\" to me.");

33 Problem Consider an array of characters containing a sentence. Knowing that the words are separated by space, count how many words are there. Also count the names (starting with a capital letter). For simplicity, we consider all the characters being letters.

34 Solution public class SolutionChar{ public static void main(string[] arg){ int count=0, countname=0; char[] array = {'A','n','a',' ','i','s',' ','h','e','r','e'}; for(int i=0;i<array.length;i++) if((character.isspace(array[i])) (i==array.length-1)) count++; else if (Character.isUpperCase(array[i])) countname++; System.out.printf("There are %d words and %d Names %n", count, countname); }} Output: There are 3 words and 1 Names

35 Strings A sequence of characters objects in the Java programming language How to create a string? String greeting = "Hello world!"; String s = new String(greeting); char[] c={'h','e','l','l','o','.'}; String S = new String(c);

36 String

37 Strings The String class is immutable The methods used on strings creates other strings accessor methods methods used to obtain information about an object String palindrome = "Dot saw I was Tod"; int len = palindrome.length();

38 Strings Reverse a palindrome char[] tempchararray = new char[len]; char[] chararray = new char[len]; for (int i = 0; i < len; i++) { tempchararray[i] = palindrome.charat(i); } for (int j = 0; j < len; j++) { chararray[j] = tempchararray[len j]; } String reversepalindrome = new String(charArray); System.out.println(reversePalindrome); Output: dot saw I was tod

39 Strings Concatenate strings string1.concat(string2); "My name is ".concat("ana"); "Hello," + " world" + "!" to span lines in source files String s="now is the time + " of roses.";

40 Converting Between Numbers and Strings Converting Strings to Numbers Number.valueOf() float a = (Float.valueOf(args[0]) ).floatvalue(); float b = (Float.valueOf(args[1]) ).floatvalue(); Number.parsePrimitive() float a = Float.parseFloat(args[0]); float b = Float.parseFloat(args[1]);

41 Converting Between Numbers and Strings Converting Numbers to Strings int i; String s1 = "" + i; String s2 = String.valueOf(i); int i; double d; String s3 = Integer.toString(i); String s4 = Double.toString(d);

42 Converting Between Numbers and Strings The number of digits before and after the decimal point public class ToStringDemo { public static void main(string[] args) { } } double d = ; String s = Double.toString(d); int dot = s.indexof('.'); System.out.println(dot + " digits before decimal point."); System.out.println( (s.length() - dot - 1) + " digits after decimal point.");

43 Manipulating Characters in a String String apal = "Niagara. O roar again!"; char achar = apal.charat(9);

44 Manipulating Characters in a String String apal = "Niagara. O roar again!"; String r =apal.substring(11,15);

45 Manipulating Characters in a String Get the character from a certain index String charat(int index) Get the substring between two indexes String substring(int beginindex, int endindex) Get the substring from a certain index until the end of string String substring(int beginindex)

46 Searching for Characters and Substrings in a String Splits a string using a separator into an array of strings String[] split(string regex) Removes leading and trailing white space String trim() String tolowercase() String touppercase()

47 Searching for Characters and Substrings in a String int indexof(int ch) int lastindexof(int ch) int indexof(int ch, int fromindex) int lastindexof(int ch, int fromindex) int indexof(string str) int lastindexof(string str) int indexof(string str, int fromindex) int lastindexof(string str, int fromindex) boolean contains(charsequence s)

48 Searching for Characters and Substrings in a String public class Filename { private String fullpath; private char pathseparator, extensionseparator; public Filename(String str, char sep, char ext) { fullpath = str; pathseparator = sep; extensionseparator = ext; } public String extension() { int dot = fullpath.lastindexof(extensionseparator); return fullpath.substring(dot + 1); }

49 Searching for Characters and Substrings in a String public String filename() { int dot = fullpath.lastindexof(extensionseparator); int sep = fullpath.lastindexof(pathseparator); return fullpath.substring(sep + 1, dot); } public String path() { int sep = fullpath.lastindexof(pathseparator); return fullpath.substring(0, sep); } }

50 Searching for Characters and Substrings in a String String fpath = "/home/mem/index.html"; Filename myhomepage = new Filename(fpath, '/', '.'); Extension = html Filename = index

51 Replacing Characters and Substrings into a String String replace(char oldchar, char newchar) String replaceall(string regex, String replacement) String replacefirst(string regex, String replacement)

52 Comparing Strings and Portions of Strings boolean endswith(string suffix) boolean startswith(string prefix) int compareto(string anotherstring) int comparetoignorecase(string str) boolean equals(object anobject) boolean equalsignorecase(string anotherstring)

53 Problem Search into a string a substring, both received as arguments when running the program. Return the beginning position. Consider a string containing, separated through ;, the name, the price and the quantity of a product. Extract them and perform the necessary type transformations.

54 Solution P1 public class SolutionStr1{ public static void main(string[] arg){ if(arg.length>=2){ String s1=arg[0]; String s2=arg[1]; int i; if((i=s1.indexof(s2))==-1) System.out.printf("\"%s\" is not included in \"%s\" %n", s2, s1); else System.out.printf("\"%s\" is included in \"%s\" starting position %d%n", s2, s1, i); } else System.out.println("Not enough arguments"); }}

55 Solution P2 public class SolutionStr2{ public static void main(string[] arg){ String s1="bread;3.5;52"; String[] array=s1.split(";"); String name=array[0]; double price=double.valueof(array[1]); int quantity = Integer.valueOf(array[2]); }} System.out.printf("Product: %s, %f, %d", name, price, quantity);

56 The Java I/O System Applications need to process some input and produce some output based on that input In Java, java.io package allows the input and output of a program primarily focused on input and output to files, network streams, internal memory buffer import java.io.*;

57 The Java I/O System I/O operations based on streams flows of data you can either read from, or write to typically connected to a data source, or data destination has no concept of an index of the read or written data cannot typically move forth and back in a stream are typically byte based Input streams Output streams

58 The Java I/O System To process data from a stream you need: Open the stream Process the data until the end of the stream (while) Close the stream

59 The Java I/O System Standard I/O System.in is an InputStream object typically connected to keyboard input of console programs System.out is a PrintStream object outputs the data you write to it to the console System.err is a PrintStream object it is normally only used to output error texts

60 The Java I/O System Input and Output - Source and Destination The terms "input" and "output" can sometimes be a bit confusing Java's IO package concerns with: the reading of raw data from a source the writing of raw data to a destination The typical sources and destinations of data: Files Pipes Network Connections In-memory Buffers (e.g. arrays) System.in, System.out, System.error

61 The Java I/O System A program that needs to read data an input stream or reader A program that needs to write data an output stream or writer An InputStream or Reader is linked to a source of data. An OutputStream or Writer is linked to a destination of data.

62 The Java I/O System Java IO Purposes and Features File Access Network Access Internal Memory Buffer Access Inter-Thread Communication (Pipes) Buffering Filtering Parsing Reading and Writing Text (Readers / Writers) Reading and Writing Primitive Data (long, int etc.) Reading and Writing Objects

63 The Java I/O System

64 The Java I/O System Some Java IO classes

65 The Java I/O System Reading text lines BufferedReader readline() Reads from an input stream until the line end Returns a reference to a String without the line end or null IOException is throw if no reading done The constructor needs an object of InputStreamReader FileInputStream if reading from a file System.in if reading from the console

66 The Java I/O System BufferedReader r_in = new BufferedReader(new InputStreamReader(new FileInputStream(file_name))); BufferedReader r_in = new BufferedReader(new InputStreamReader (System.in)); line = r_in.readline(); while(line!= null) {Do something line = r_in.readline();} r_in.close();

67 The Java I/O System The PrintStream class: Enables the writing of formatted data to an underlying OutputStream Contains the print()/println() to print a string Contains the powerful format() and printf() methods The constructor needs an object of FileOutputStream (write a file as a stream of bytes)

68 The Java I/O System PrintStream w_out = new PrintStream (new FileOutputStream(file_name)); w_out.println( ); w_out.print(true); w_out.print((int) 123); w_out.print((float) ); w_out.printf(locale.uk, "Text + data: %1$", 123); w_out.close();

69 The Java I/O System Streams and Readers / Writers need to be closed properly r_in.close( ); w_out.close( ); public static void main (String[ ] arg) throws IOException { }

70 The Java I/O System

71 The Java I/O System Scanner Can parse primitive types and strings using regular expressions Breaks its input into tokens using a delimiter pattern, which by default matches whitespace Has various next methods to convert the tokens Scanner sc = new Scanner(System.in); int i = sc.nextint(); Scanner sc = new Scanner(System.in).useDelimiter( );

72 The Java I/O System Scanner Scanner sc = new Scanner(new File("myNumbers")); while (sc.hasnextlong()) { long along = sc.nextlong(); } System.out.println("Enter your username: "); Scanner scanner = new Scanner(System.in); String username = scanner.nextline(); System.out.println("Your username is " + username);

73 The Java I/O System Scanner Problems: a scanning operation may block waiting for input. is not safe for multithreaded use without external synchronization. doesn t work well reading strings and numbers with the same scanner Import java.util.scanner

74 References The Java Tutorials. Learning the Java Language. data/index.html Java IO Tutorial. Java Scanner /java/util/scanner.html