13. class Apublic int f(int x)return x+1;class B extends Apublic int f(int x)return x*x;public class wwppublic static void main(String args)A a=new B();int m=a.f(10);System.out.println(m);答案：14. class Aint x;public void setX(int x)this.x=x;int getX()return x;class Bpublic void f(A a)a.setX(100);public class wwppublic static void main(String args)A a=new A();a.setX(8);System.out.println(a.getX();B b=new B();b.f(a);System.out.println(a.getX();答案：15.注意事项：首先，在接口中要知道每个接口中的方法是什么类型的；其次，要注意非静态的方法不能再静态方法中调用。interface footvoid 食品(String s);class fr implements footpublic void 食品(String s)System.out.println(s);class ve implements footpublic void 食品(String s)System.out.println(s);public class wwppublic static void main(String args)foot ft;ft=new fr();ft.食品(苹果);ft=new ve();ft.食品(生菜);答案：16. class Aint m;void f()for(m=65;m91;m+)System.out.print(char)m+ );for(m=97;m123;m+)System.out.print(char)m+ );System.out.println( );class B extends Aint i;void g()for(i=913;i930;i+)System.out.print(char)i+ );for(i=931;i938;i+)System.out.print(char)i+ );for(i=945;i962;i+)System.out.print(char)i+ );for(i=963;i1000)MyException exception=new MyException(m);throw exception;elseSystem.out.println(m);public class testpublic static void main(String args)int m;student stul=new student();m=987;trystul.speak(m);m=1234;stul.speak(m);catch(MyException e)e.showstrl(); 18. class Apublic int f(int a,int b)if(ab)int temp=0;temp=a;a=b;b=temp;int r=a%b;while(r!=0)a=b;b=r;r=a%b;return b;class B extends Apublic int f(int a,int b)int m;m=super.f(a,b);return (a*b)/m;public class wpublic static void main(String args)A a=new A();System.out.println(18和102 的最大公约数是:+a.f(18,102);B b=new B();System.out.println(18和102的最小公倍数是:+b.f(18,102);答案：