copy.dept_change( CSE ); // Original Objects also changed

Transcription

1 UNIT - III

2 Topics Covered The Object class Reflection Interfaces Object cloning Inner classes Proxies I/O Streams Graphics programming Frame Components Working with 2D shapes.

3 Object Clone

4 Object Cloning in Java: When a copy of a variable is made, the original and the copy objects have references to the same object. This means a change to either variable also affects the other. Student original = new Student(1001, CCET ); Student copy = original; // taking copy copy.dept_change( CSE ); // Original Objects also changed Original = Student Copy = In order to copy an old object into another new object which should not refer to the old object but the values has to copied to a new reference then use the clone method. The object cloning is a way to create exact copy of another object without affecting one another. Student copy = original.clone(); copy.dept_change( CSE ); //Original unchanged Original = Student Copy = Student

5 The java.lang.cloneable interface must be implemented by the class whose object clone we want to create. If we don't implement Cloneable interface, clone() method generatesclonenotsupportedexception. The clone() method is a protected method defined in the Object class. Syntax of the clone() method is as follows: Syntax: Why use clone() method? protected Object clone() throws CloneNotSupportedException The clone() method saves the extra processing task for creating the exact copy of an object. If we perform it by using the new keyword, it will take a lot of processing to be performed that is why we use object cloning. Advantage of Object cloning Less processing task. Types of Cloning: 1. Shallow Cloning Default Cloning method 2. Deep Cloning To do cloning a class must Implement the Cloneable interface, and Redefine the Clone method with the public access modifier.

6 1. Shallow Copy: Shallow Cloning means field-by-field copying. If each and every field is numbers or basic types then there is no problem. If the fields in turn are objects of another class, then field-by-field copying will make the original and copy objects to refer to the same sub-objects. Original = Student String name = values int Stdid = values Date DOB = values String Copy = Student String name = values int Stdid = values Date DOB = values Date

7 In shallow copy, a new object is created which contains the exact copy of the values in the original object. Shallow copy follows the bit-wise copy approach. In shallow copy if the field is a memory address, then the address is copied. Thus if the address is changed by one object, the change gets reflected everywhere. Figure 1: The flow chart describes shallow copy In this figure, the object - mainobj1 has fields field1 of a primitive type say int, and an object of type String When we do a shallow copy of mainobj1, mainobj2 is created with field2 of type int which contains the copied value of field1 but the String object in mainobj2 - still points to objstr itself. Since field1 is a primitive data type, the value of it is copied into field2. But since objstr is an object, mainobj2 is pointing to the same address of objstr. So any changes made to objstr via mainobj1 get reflected in mainobj2.

8 Example 1 class Student implements Cloneable String name; Student(String n) name = n; public void setname(string s) name = s; public String getname() return name; public Object clone() try //shallow copy return super.clone(); catch(clonenotsupportedexception e) return null;

9 public class ShallowClone public static void main(string[] args) //Original Object Student original = new Student("Java Programming"); System.out.println("Original Object: " + original.getname()); //Clone Object Student cloned = (Student) original.clone(); System.out.println("Cloned Object: " + cloned.getname()); original.setname("advanced Java"); System.out.println("Original Object after it is updated: " + original.getname()); System.out.println("Cloned Object after updating original object: "+ cloned.getname()); Output: Original Object: Java Programming Cloned Object: Java Programming Original Object after it is updated: Advanced Java Cloned Object after updating original object: Advanced Java

10 Example 2 class Subject String name; String getname() return name; void setname(string s) name = s; Subject(String s) name = s; class Student implements Cloneable //Contained object Subject subj; String name; Student(String s, String sub) name = s; subj = new Subject(sub); String getname() return name; void setname(string s) name = s; Subject getsubj() return subj; public Object clone() //shallow copy try return super.clone(); catch (CloneNotSupportedException e) return null;

11 public class ShallowCopy public static void main(string[] args) //Original Object Student stud = new Student("John", "Algebra"); System.out.println("Original Object: " + stud.getname() + " - " + stud.getsubj().getname()); //Clone Object Student clonedstud = (Student)stud.clone(); System.out.println("Cloned Object: " + clonedstud.getname() + " - " + clonedstud.getsubj().getname()); stud.setname("dan"); stud.getsubj().setname("physics"); System.out.println("Original Object after it is updated: " + stud.getname() + " - " + stud.getsubj().getname()); System.out.println("Cloned Object after updating original object: " + clonedstud.getname() + " - " + clonedstud.getsubj().getname()); Output: Z:\Java Programs\Examples\Cloning>javac ShallowCopy.java Z:\Java Programs\Examples\Cloning>java ShallowCopy Original Object: John - Algebra Cloned Object: John - Algebra Original Object after it is updated: Dan - Physics Cloned Object after updating original object: John - Physics Z:\Java Programs\Examples\Cloning>

12 2. Deep Cloning: Cloning of Subclasses is called as Deep Cloning. In deep copy, not only all the fields of an object are copied, all the dynamically allocated memory address which are pointed by that object are also copied. When the copied object contains some other object its references are copied recursively in deep copy. It s typical restriction of the protected access. In this figure, the object mainobj1 has fields field1 a primitive data type say int, and an object of type String When we do a deep copy of mainobj1, mainobj2 is created with field2 containing the copied value of field1 and objstr2 is created which contains the copied value of objstr1 So any changes made to objstr1 in mainobj1 will not reflect in mainobj2.

13 Example 1 class Student implements Cloneable private String name; Student(String n) name = n; public String getname() return name; public void setname(string s) name = s; public Object clone() //Deep copy Student s = new Student(name); return s;

14 public class DeepClone public static void main(string[] args) //Original Object Student original = new Student("Java Programming"); System.out.println("Original Object: " + original.getname()); //Clone Object Student cloned = (Student)original.clone(); System.out.println("Cloned Object: " + cloned.getname()); original.setname("advanced Java"); System.out.println("Original Object after it is updated: "+ original.getname()); Output: System.out.println("Cloned Object after updating original object: "+ cloned.getname() ); Original Object: Java Programming Cloned Object: Java Programming Original Object after it is updated: Advanced Java Cloned Object after updating original object: Java Programming

15 Example 2 class Subject private String name; public String getname() return name; public void setname(string s) name = s; Subject(String s) name = s; class Student implements Cloneable //Contained object Subject subj; String name; Subject getsubj() return subj; String getname() return name; void setname(string s) name = s; Student(String s, String sub) name = s; public Object clone() subj = new Subject(sub); //Deep copy Student s = new Student(name, subj.getname()); return s;

16 public class DeepCopy public static void main(string[] args) //Original Object Student stud = new Student("John", "Maths"); System.out.println("Original Object: " + stud.getname() + " - " + stud.getsubj().getname()); //Clone Object Student clonedstud = (Student) stud.clone(); System.out.println("Cloned Object: " + clonedstud.getname() + " - " + clonedstud.getsubj().getname()); stud.setname("dan"); stud.getsubj().setname("physics"); System.out.println("Original Object after it is updated: " + stud.getname() + " - " + stud.getsubj().getname()); System.out.println("Cloned Object after updating original object: " + clonedstud.getname() + " - " + clonedstud.getsubj().getname()); Output: Z:\Java Programs\Examples\Cloning>java DeepCopy Original Object: John - Maths Cloned Object: John - Maths Original Object after it is updated: Dan - Physics Cloned Object after updating original object: John - Maths Z:\Java Programs\Examples\Cloning>

17 Inner Classes

18 Inner Classes: A class declared inside a class is known as inner class. Syntax of Inner class class Outer_class_Name class Nested_class_Name... There are three reasons to have an inner class: Inner classes represent a special type of relationship that is it can access all the members (data members and methods) of outer class including private. Inner classes are used to develop more readable and maintainable code because it logically group classes and interfaces in one place only. Code Optimization: It requires less code to write.

19 There are several Inner Classes. They are: Member Inner Class Anonymous Inner Class Local Inner Class Static Inner Class 1. Member Inner Class: A class that is declared inside a class but outside a method is known as member inner class. It is present common inside so that it can be accessed by all methods of the outer class. The Outer Class Object can have rights to access its members and the inner class members along with the inner class object. How to access Member Inner class From within the class From outside the class

20 Example 1 : within the class class Outer1 private int a=10; class Inner1 void msg() System.out.println( The value for a is "+data); void display() Inner1 in=new Inner1(); in.msg(); public static void main(string args[]) Outer1 obj=new Outer1(); obj.display(); Output: The value for a is 10

21 Example 2 : outside the class class Outer2 private int a=20; class Inner2 void msg() System.out.println("The value for a is " +a); class TestOuter2 public static void main(string args[]) Outer2 out=new Outer2(); Outer2.Inner2 in=out.new Inner2(); in.msg(); Output: The value for a is 20

22 Example 3 : class Inner3 int a; public void disp_inner() System.out.println("Inner Class Method"); class Outer3 Inner3 in = new Inner3(); int b; public void disp_outer() System.out.println("Outer Class Method");

23 class InnerOuter3 public static void main(string args[]) int c; Outer3 o = new Outer3(); o.b = 20; o.disp_outer(); o.in.a = 10; o.in.disp_inner(); c = o.b + o.in.a; System.out.println( The Value for c is : "+c); Output: Outer Class Method Inner Class Method The Value for c is : 30

24 2. Local Inner Class: A class that is created inside a method is known as local inner class. If you want to invoke the methods of local inner class, you must instantiate this class inside the method. Their scope is always restricted to the block in which they are declared. Local classes have a great advantage: they are completely hidden from the outside world not even other code in the Outer Class can access them. Local variable can't be private, public or protected. class Outer1 public void disp_outer() System.out.println("Outer Class Method"); class Inner1 void disp_inner() System.out.println("Inner Class Method"); Inner1 in = new Inner1(); in.disp_inner();

25 public static void main(string[] args) Outer1 out= new Outer1(); out.disp_outer(); Output: Outer Class Method Inner Class Method 3. Anonymous Inner Class: When using local inner classes, we can create any number of Objects for the Inner Class. If to make only a single object of a class, no need to give the class name. Such a class is called an Anonymous Inner Class. Here, Interface can be used, the inner class implements that interface. Outer Class s method define the implementation of the inner class within its own member function.

26 class Outer interface Interface public void disp_interface(); public void disp_outer() class Inner implements Interface public void disp_interface() System.out.println("Interface Method Invoked inside Inner Class"); Interface inter1 = new Inner();

27 Interface inter2 = new Interface() public void disp_interface() System.out.println("Interface Method in Object"); ; inter1.disp_interface(); inter2.disp_interface(); class AnonymousClass public static void main(string args[]) Outer o = new Outer(); o.disp_outer(); Output: Interface Method Invoked inside Inner Class Interface Method in Object

28 4. Static Inner Class: To hide the inner class inside another, but don t need the inner class to have a reference to the outer class object, static inner class can be used. The generation of that reference can be suppressed by declaring the inner class static. class Outer static class Inner class StaticInner Output: void display() public static void main(string[] args) System.out.println("Inner class reference is: " + this); Outer.Inner n = new Outer.Inner(); n.display(); Inner class reference is: Outer$Inner@19821f

29 Object Class: The Object class is the parent class of all the classes in java by default. In other words, it is the topmost class of java. The Object class is beneficial if you want to refer any object whose type you don't know. Notice that parent class reference variable can refer the child class object, know as upcasting. Let's take an example, there is getobject() method that returns an object but it can be of any type like Employee, Student etc., we can use Object class reference to refer that object. For example: Syntax: Object obj = new Student(); Object obj=getobject(); A variable of type Object is only useful as a generic holder for arbitrary values. Method public int hashcode() Description returns the hashcode number for this object. public boolean equals(object obj) compares the given object to this object. protected Object clone() throws CloneNotSupportedException public String tostring() protected void finalize()throws Throwable creates and returns the exact copy (clone) of this object. returns the string representation of this object. is invoked by the garbage collector before object is being garbage collected.

30 I/O STREAMS

31 I/O STREAMS The Java I/O means Java Input/Output. It is provided by the java.io package. This package has an InputStream and OutputStream. Java InputStream is defined for reading the stream, byte stream and array of byte stream. A Stream is a sequence of data. It is composed of bytes. It is basically a channel on which the data flow from sender to receiver. An input object that reads the stream of data from a file is called input stream and the output object that writes the stream of data to a file is called output stream. Java implements streams within the classes that are defined in java.io package. Types of streams Character Stream Byte Stream Character Stream The two super classes in character stream are Reader and Writer. Byte Stream The two super clasess in byte stream are InputStream and OutputStream from which most of the other classes are derived.

32 Character Stream Classes Character stream is defined by using two abstract class at the top of hierarchy, they are Reader and Writer. Some important Character Stream classes:

33 Byte Stream Classes Byte stream is defined by using two abstract class at the top of hierarchy, they are InputStream and OutputStream. Some important Byte Stream classes:

34 I/O HANDLING USING CHARACTER STREAM Reading Console Input: BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); Reading Characters from Console: int read( ) throws IOException Example import java.io.*; public class BRRead public static void main(string args[]) throws IOException char c; BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); System.out.println("Enter characters, 'q' to quit."); // read characters do c = (char) br.read(); System.out.println(c); while(c!= 'q');

35 OUTPUT: Z:\Java Programs\Examples\IOStreams>javac BRRead.java Z:\Java Programs\Examples\IOStreams>java BRRead Enter characters, 'q' to quit. ABC 2013q A B C q Z:\Programs\javapgm\RUN\STREAMS>

36 Reading Strings from Console: String readline( ) throws IOException Example import java.io.*; public class BRReadLines public static void main(string args[]) throws IOException BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); String str; System.out.println("Enter lines of text."); System.out.println("Enter 'end' to quit."); do str = br.readline(); System.out.println(str); while(!str.equals("end"));

37 OUTPUT: Z:\Java Programs\Examples\IOStreams>javac BRReadLines.java Z:\Java Programs\Examples\IOStreams>java BRReadLines Enter lines of text. Enter 'end' to quit. WELCOME CCET WELCOME CCET 2013 end 2013 end hi hi end end Z:\Programs\javapgm\RUN\STREAMS>

38 Writing Console Output: void write(int byteval) Example import java.io.*; // Demonstrate System.out.write(). public class WriteDemo public static void main(string args[]) int b; b = 'A'; System.out.write(b); System.out.write('\n'); Output: Z:\Java Programs\Examples\IOStreams>javac WriteDemo.java Z:\Java Programs\Examples\IOStreams>java WriteDemo A

39 OUTPUT STREAM READING AND WRITING FILES

40 INPUT STREAM

41 I/O HANDLING USING BYTE STREAM FileInputStream: InputStream f = new FileInputStream( Z://java//hello"); File f = new File( Z://java//hello"); InputStream f = new FileInputStream(f); FileOutputStream: OutputStream f = new FileOutputStream( Z://java//hello") File f = new File( Z://java//hello"); OutputStream f = new FileOutputStream(f);

42 FILEINPUTSTREAM Example 1 import java.io.*; class FileInputStream1 public static void main (String args[]) throws IOException int n; InputStream ips=new FileInputStream("Z:\\Java Programs\\Examples\\IOStreams\\BRRead.java"); System.out.println("Total Bytes: "+(n=ips.available())); int m = n-390; System.out.println("\nReading first " +m+ " bytes at a time"); for(int i=0;i<m;i++) System.out.print((char)ips.read()); System.out.println("\n Skipping some text"); ips.skip(n/2); System.out.println("\n Still Available: " +ips.available()); ips.close();

43 Output Z:\Java Programs\Examples\IOStreams>javac FileInputStream1.java Z:\Java Programs\Examples\IOStreams>java FileInputStream1 Total Bytes: 394 Reading first 4 bytes at a time impo Skipping some text Still Available: 193 Z:\Java Programs\Examples\IOStreams>

44 FILEINPUTSTREAM Example 2 import java.io.*; class FileInputStream2 public static void main(string args[]) throws Exception FileInputStream fn = new FileInputStream("Z:\\Java Programs\\Examples\\IOStreams\\Input.txt"); int i; while((i=fn.read())!= -1) System.out.println((char)i); fn.close();

45 Output Z:\Java Programs\Examples\IOStreams>javac FileInputStream2.java Z:\Java Programs\Examples\IOStreams>java FileInputStream2 W e l c o m e t o C C E T Z:\Java Programs\Examples\IOStreams>

46 FILEOUTPUTSTREAM Example 1 import java.io.*; class FileOutStream1 public static void main (String args[]) throws Exception String text="hello, " + "Welcome to Chettinad"; byte b[] = text.getbytes(); OutputStream fobj = new FileOutputStream("Z:\\Java Programs\\Examples\\IOStreams\\Output.txt"); for(int i=0;i<b.length;i++) fobj.write(b[i]); System.out.println("\n The data is written to the file"); fobj.close();

47 Output Z:\Java Programs\Examples\IOStreams>javac FileOutStream1.java Z:\Java Programs\Examples\IOStreams>java FileOutStream1 The data is written to the file Z:\Java Programs\Examples\IOStreams> Output.txt Hello, Welcome to Chettinad

48 FILEOUTPUTSTREAM Example 2 import java.io.*; class FileOutStream2 public static void main(string args[]) throws Exception FileOutputStream fout = new FileOutputStream("Z:\\Java Programs\\Examples\\IOStreams\\Out.txt"); String s = "JAVA PROGRAMMING"; byte b[] = s.getbytes(); fout.write(b); fout.close(); System.out.println("Success...");

49 Output Z:\Java Programs\Examples\IOStreams>javac FileOutStream2.java Z:\Java Programs\Examples\IOStreams>java FileOutStream2 Success... Z:\Java Programs\Examples\IOStreams> Z:\Java Programs\Examples\IOStreams>type out.txt JAVA PROGRAMMING