![Implementing Interfaces
To implement an interface, include the implements
clause in a class definition, and then create the
methods defined by the interface.
The general form of a class that includes the
implements clause looks like this:
class classname [extends superclass] [implements
interface [,interface...]]
{
// class-body
}](https://image.slidesharecdn.com/interface-250212075332-b065161b/85/working-with-interfaces-in-java-programming-4-320.jpg)
![Example
interface MyInterface
{
public void method1();
public void method2();
}
class XYZ implements MyInterface
{
public void method1()
{ System.out.println("implementation of method1");
}
public void method2()
{ System.out.println("implementation of method2");
}
public static void main(String arg[])
{
XYZ obj = new XYZ();
obj. method1();
obj. method2();
}
}](https://image.slidesharecdn.com/interface-250212075332-b065161b/85/working-with-interfaces-in-java-programming-5-320.jpg)
![Accessing Implementations Through Interface References
interface MyInterface
{
public void method1();
public void method2();
}
class XYZ implements MyInterface
{
public void method1()
{ System.out.println("implementation of method1");
}
public void method2()
{ System.out.println("implementation of method2");
}
public static void main(String arg[])
{
MyInterface obj = new XYZ();
obj. method1();
obj. method2();
}
}](https://image.slidesharecdn.com/interface-250212075332-b065161b/85/working-with-interfaces-in-java-programming-6-320.jpg)
![class InterfaceExtend
{
public static void main(String arg[])
{
MyClass ob = new MyClass();
ob.meth1();
ob.meth2();
ob.meth3();
}
}](https://image.slidesharecdn.com/interface-250212075332-b065161b/85/working-with-interfaces-in-java-programming-11-320.jpg)
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working with interfaces in java programming
- 1. INTERFACE An interface is a list of constants and method headers. The methods are not implemented in the interface. A class that implements an interface must implement each of the methods listed in the interface.
- 2. Defining an Interface the general form of an interface access interface interface_name { return-type method-name1(parameter-list); return-type method-name2(parameter-list); type final-varname1 = value; type final-varname2 = value; // ... return-type method-nameN(parameter-list); type final-varnameN = value; }
- 3. Example interface MyInterface { //All the methods are public abstract by default public void method1(); public void method2(); }
- 4. Implementing Interfaces To implement an interface, include the implements clause in a class definition, and then create the methods defined by the interface. The general form of a class that includes the implements clause looks like this: class classname [extends superclass] [implements interface [,interface...]] { // class-body }
- 5. Example interface MyInterface { public void method1(); public void method2(); } class XYZ implements MyInterface { public void method1() { System.out.println("implementation of method1"); } public void method2() { System.out.println("implementation of method2"); } public static void main(String arg[]) { XYZ obj = new XYZ(); obj. method1(); obj. method2(); } }
- 6. Accessing Implementations Through Interface References interface MyInterface { public void method1(); public void method2(); } class XYZ implements MyInterface { public void method1() { System.out.println("implementation of method1"); } public void method2() { System.out.println("implementation of method2"); } public static void main(String arg[]) { MyInterface obj = new XYZ(); obj. method1(); obj. method2(); } }
- 7. Variables in Interface interface doesn't allow you to declare any instance variables. You can declare a constant variable, using static final. By default these variables are public. Example interface MyInterface { int aConstant = 32; // a constant (public static final, by default) double pi = 3.14159; // a constant (public static final, by default) void methodA( int x ); // a method header (public, by default) double methodB(); // a method header (public, by default) }
- 8. interface SomeInterface { public final int x = 32; public double y;// public double addup( ); } Inspect the interface. Is it correct?
- 9. Interfaces can be extended One interface can inherit another by use of the keyword extends. The syntax is the same as for inheriting classes. Example interface A { void meth1(); void meth2(); } // B now includes meth1() and meth2() -- it adds meth3(). interface B extends A { void meth3(); }
- 10. When a class implements an interface that inherits another interface, it must provide implementations for all methods. Example interface A { void meth1(); void meth2(); } interface B extends A { void meth3(); } // This class must implement all of A and B class MyClass implements B { public void meth1() { System.out.println("Implement meth1()."); } public void meth2() { System.out.println("Implement meth2()."); } public void meth3() { System.out.println("Implement meth3()."); } }
- 11. class InterfaceExtend { public static void main(String arg[]) { MyClass ob = new MyClass(); ob.meth1(); ob.meth2(); ob.meth3(); } }