Java Interview 基本概念

1. abstract class

abstract class can have anything a normal class can have plus abstract method

public abstract class Test11 {

    public int a;

    private int b;

    public abstract void f1();

    public void f2() {

    }
}

2.interface

only final variable and abstract method,

can extends another interface, can extends more than 1 interface

cannot extends class or implement interface

public interface Inter2 extends Inter1, Inter2 {
    public int a = 1;

    public abstract void f1();

    public void f2();
}

 3. static nested class & inner class

http://docs.oracle.com/javase/tutorial/java/javaOO/nested.html

http://stackoverflow.com/questions/70324/java-inner-class-and-static-nested-class

Static nested class:

a static nested class is behaviorly a top level class

https://www.codeofaninja.com/2013/09/android-viewholder-pattern-example.html

public class StaticNestedOuter {
    public static void main(String[] args) {
        StaticNestedOuter.StaticNestedClass sn = new StaticNestedClass();
    }
    static class StaticNestedClass {
    }
}

Inner class:

public class OuterClass {
    private String baz;

    public static void main(String[] args) {
        OuterClass oc = new OuterClass();
        InnerClass ic = oc.new InnerClass();
    }

    public void foo() {
        InnerClass ic2 = new InnerClass();
    }

    class InnerClass {
        public void print() {
            // access outer member in 2 ways
            System.out.print(OuterClass.this.baz);
            System.out.print(baz);
        }
    }
}