（1）
package com.cvit;
public interface Flyer{ public void takeOff(); public void land(); public void fly(); }（2）
package com.cvit;
public class Airplane implements Flyer{ public void takeOff(){ System.out.println("airplane takeOff"); } public void land(){ System.out.println("airplane land"); } public void fly(){ System.out.println("airplane fly"); }} （3）SuperClass.java
package com.cvit;
class SuperClass
{
int x;
public void SuperClass()
{
x=4
System.out.println("n subClass : x =" ,x);
}
public void aMethod()
{
System.out.println("in superClass.aMethod()");
}
}
（4）
package com.cvit;
class SuperClass { public int x; public SuperClass(){ x=4; System.out.println("in superClass: x="+x); } public void aMethod(){ System.out.println("in superClass.aMethod()"); }} class SubClass1 extends SuperClass { public int x; public SubClass1(){ x=6; System.out.println("in subClass: x="+x); } public void aMethod(){ System.out.println("in SubClass1.aMethod()");System.out.println("super.x = " +super.x+", sub.x=%d" +this.x);
} public int aMethod(int a,int b){ return a+b; }}（5）
package com.cvit;
public class SubClass2{ public void aMethod(){ System.out.println("in SubClass2.aMethod()");} public int aMethod(int a,int b){ return a+b; }}
(6)
package com.cvit;
public class SubClass3{ public void aMethod(){ System.out.println("in SubClass3.aMethod()");} public int aMethod(int a,int b){ return a+b; }}
(7)
package com.cvit;
public class Main { public static void chooseClass(SubClass2 sub2){ } public static void chooseClass(SubClass3 sub3){ } public static void main(String args[]){ int x=7; Airplane airplane=new Airplane(); airplane.takeOff(); SubClass1 sub1=new SubClass1(); sub1.aMethod(); x=sub1.aMethod(x,x); airplane.fly(); SubClass2 sub2=new SubClass2(); SubClass3 sub3=new SubClass3(); Main.chooseClass(sub2); x=sub2.aMethod(x,x); Main.chooseClass(sub3); x=sub2.aMethod(x,x); }}