Java – Interface before JDK8

Interface (before JDK7):

• Interface is a collection of abstract methods.
• Interface methods are by default public and abstract.
• Any class can implement interface
• Implemented class override abstract methods.

Note: The object address of implemented class assign to Interface type reference variable.

InterfaceName obj = new ImplementedClass();

interface Test {             void m1(); // public abstract } class Demo implements Test {             public void m1()             {                         System.out.println(“m1…”);             } } class Main {             public static void main(String[] args)             {                         Test obj = new Demo();  // upcasting                         obj.m1();             } }

• Interface variables are by default public static final.
• We must initialize variables defined in interface.
• We cannot modify the variables as they are final.

interface Code {             int a = 10;  // public static final } class Main {             public static void main(String[] args)             {                         System.out.println(“a value : ” + Code.a);                         Code.a = 20 ; // Error : final variable cannot be modified             } }