Mutable and immutable classes

1. Mutable and immutable classes

2. AGENDA Introduction Mutable Classes Immutable Classes Cloning and Mutable Conclusion

3. Introduction An Immutable object is a kind of object whose state cannot be modified after it is created where a Mutable Object can be modified after it is created.

4. Immutable A class that contains methods (other than constructors) that change any of the data in an object of the class is called immutable classes and object of the class are called immutable objects . Strings are immutable class. In Java, objects are referred by references. If an object is known to be immutable, the object reference can be shared.

5. For example, Boolean , Byte , Character , Double , Float , Integer , Long , Short , and String are immutable classes in Java. An immutable object is one whose externally visible state cannot change after it is instantiated. The String , Integer , and BigDecimal classes in the Java class library are examples of immutable objects -- they represent a single value that cannot change over the lifetime of the object.

6. Sample Program Class Pro1 { public static void main(String[] args ) { String str = "WELCOME"; System. out.println ( str ); str.toLowerCase (); //Doesn’t impact on original content of Str System. out.println ( str ); Output } WELCOME } WELCOME

7. Modified Program class Pro1 { public static void main(String[] args ) { String str = “WELCOME"; System.out.println ( str ); String str1 = str.toLower (); System.out.println (str1); Output } WELCOME } welcome

8. Mutable A class that contains public methods or input methods that can change the data in an object of the class is called mutable classes and the object of the class are called mutable objects . The class Date is an example of a mutable class. When defining any methods , that method should not return a reference to a mutable object. Instead use a copy constructor to return a reference to a completely independent copy of the mutable object.

9. A String Buffer is a string that can be changed. String Buffers are Mutable , they’re not inherently thread safe and thus many of the methods of String Buffer class are synchronized. The StringBuffer has the methods Append( ) Insert ( )

10. Mutable Objects in AWT and Swing The java.awt package defines several classes that encapsulate geometric information. AWT Geometry Classes CLASS DESCRIPTION Point (x , y) location in space Dimension Component width and height Insets Representation of the Borders of a container Rectangle Area in a coordinate space

11. The java.awt.Component and java.awt.Container classes define methods to access certain geometric information. public Point getLocation (); public void setLocation ( Point loc); public Dimension getSize (); public void setSize (Dimension size); public Insets getInsets (); public void setInsets (Insets insets ); public Rectangle getBounds (); public void setBounds (Rectangle bounds);

12. Cloning and mutable objects All classes that implement Cloneable should override clone with a public method whose return type is the class itself. This method should call super.clone and then fix any fields that need to be fixed. Typically this means copying any mutable objects that comprise the internal deep structure of object being cloned and replacing the clone’s references to these objects with references to the copies.

13. Reference Absolute JAVA – Walter Savitch Effective Java – Joshua Bloch Websites www.sun.com www.google.com

14. THANK YOU