What is partial interface, how use variables in interface and when to extend interface
Partial interface Implementations
If a class implements an interface but does not fully implement its methods, then that class must be declared as abstract. For example:
interface MyInterface {
void callback(int param);
// w w w .j a v a2 s . com
void show();
}
abstract class Incomplete implements MyInterface {
int a, b;
public void show() {
System.out.println(a + " " + b);
}
}
Variables in Interfaces
We can use interface to organize constants.
interface MyConstants {
int NO = 0;//from ww w. j a v a2 s. c om
int YES = 1;
}
class Question implements MyConstants {
int ask() {
return YES;
}
}
public class Main implements MyConstants {
static void answer(int result) {
switch (result) {
case NO:
System.out.println("No");
break;
case YES:
System.out.println("Yes");
break;
}
}
public static void main(String args[]) {
Question q = new Question();
answer(q.ask());
}
}
The output:
Extend Interface
One interface can inherit another interface with the keyword extends.
interface IntefaceA {
void meth1();//from w ww . j av a 2 s .c o m
void meth2();
}
interface IntefaceB extends IntefaceA {
void meth3();
}
class MyClass implements IntefaceB {
public void meth1() {
System.out.println("Implement meth1().");
}
public void meth2() {
System.out.println("Implement meth2().");
}
public void meth3() {
System.out.println("Implement meth3().");
}
}
public class Main {
public static void main(String arg[]) {
MyClass ob = new MyClass();
ob.meth1();
ob.meth2();
ob.meth3();
}
}
The output:
