1: class Super{2: public int getValue() {return 2019;}3: }

1.1: class Super{2: public int getValue() {return 2019;}3: }4: public class Sub extends Super{5: 6:}下列选项中，（）放在第5行会引起编译错误？选项： A:public void getValue() { }; B:public void getValue(int a) { }; C:public int getValue() {return 2016;}; D:public double getValue(double a,double b) { return a+b; }

2. 问题.1： class Super{2： public float getNum( ) {return 6.0f;}3： }4： public class Sub extends Super5： {6： 7： }以下选项中，（）放在第6行会引起编译错误。选项： A:public float getNum( ) {return 4.0f;} B:public void getNum( ) { } C:public void getNum(double d) { } D:public double getNum(double d) {return 6.0+d;}

3.现有如下代码 1： class Super{ 2： public float getNum(){return 3.0f;} 3： } 4： public class Sub extends Super{ 5： 6： } 在第5行加入下列哪行代码后会导致程序编译错误选项： A、public float getNum(){return 4.0f;} B、public void getNum(){} C、public void getNum(double d){} D、public double getNum(float d){return 4.0d;}

4.有下面类的定义：class Super{ public float getNum(){ return 3.0f;}}public class Sub extends Super{ ;}下面方法放在画线处会发生编译错误的是（） A、public float getNum(){return 4.0f;}B、public void getNum(){}C、 public void getNum(double d){}D、 public double getNum(float x){return 4.0d;

5.给定如下Java 代码，下列（）选项可以加入到Sub类中，并能保证编译正确。Class Super{public float getNum(){return 3.0f;}}public class sub extends Super{} 选项： A、public float getNum(){return 4.0f;} B、public void getNum(){} C、public getNum(double d){} D、public double getNum(flout d){return 4.0d;}

6.有下面类的定义： Class Super{ Public float getNum(){return 3.0f} } Public class Sub extends Super{ } 下面方法放在画线处会发生编译错误的是（）选项： A:public float getNum(){return 4.0f;} B:public void getNum(double d){ C:public void getNum(){} D:public double getNum(float d){return 4.0d;}

7.有下面类的定义: class Super{ public float getNum(){ return 3.0f; } } public class Sub extends Super{ ; } 下面方法放在画线处会发生编译错误的是()A.public float getNum(){return 4.0f;}B.public void getNum(){}C.public void getNum(double d){}D.public double getNum(float x){return 4.0d;}

8.在下面程序的第6行补充上下列哪个方法,会导致在编译过程中发生错误 1) class Super{ 2) public float getNum(){ 3) return 3.0f; 4) } } 5) public class Sub extends Super{ 6) 7) } 选项： A:public float getNum(){retun 4.0f;} B:public void getNum(){} C:public void getNum(double d){} D:public double getNum(float d){ retun 4.0f ;}

9.现有如下代码class Super{ public float getNum(){return 3.0f;} } public class Sub extends Super{ //【代码】} 在【代码】标注行加入下列哪行代码后会导致程序编译错误选项： A、public float getNum(){return 4.0f;} B、public void getNum(){} C、public void getNum(double){} D、public double getNum(float d){return 4.0d;}

10.中国大学MOOC: public class Test{ public static void main(String[ ] args) { int result =???; System.out.println(result); } public static int operate(double a, int b) { return 10*(int)(a+b); } public static int operate(int a, double b) { return 100*(int)(a+b); } public static int operate(double a, double b) { return 1000*(int)(a+b); }}???处填入（）时，编译程序会出错。

11.在下面程序的第6行补充上下列哪个方法,会导致在编译过程中发生错误?1) class Super{2) public float getNum(){3) return 3.0f;4) }}5) pubhc class Sub extends Super{6)7) }选项： A:public float getNum(){retun 4.0f;} B:public void getNum(){} C:public void getNum(double d){} D:public double getNum(float d){ retun 4.0f ;}

12.给定如下Java代码,下列哪个选项可以加入到Sub类中,并能保证编译正确。 class Super{ public float getNum(){ return 3.0f; } } public class Sub extends Super{ }A.public float getNum(){ return 4.0f;}B.public void getNum(){}C.public getNum(double d){}D.public double getNum(float d) {return 4.0d;}

13.在下面程序的第6行补充上下列哪个方法,会导致在编译过程中发生错误?1) class Super{2) public float getNum(){3) return 3.0f;4) }}5) pubhc class Sub extends Super{6)7) } 选项： A:public float getNum(){retun 4.0f;} B:public void getNum(){} C:public void getNum(double d){} D:public double getNum(float d){ retun 4.0f ;}

14.3、下面哪些方法置于指定位置会导致编译错误 public class J_Super { public float getNum(){ return 3.0f; } public class J_Sub extends J_Super{ //指定位置 } }选项： A:A public float getNum(){return 4.0f;}; B:B public void getNum(){}; C:C public void getNum(double d){}; D:D public double getNum(float d){return 4.0d; }

15.有如下java代码:class super{public float getNum(){return 3.0f;}}public class sub extends super{_______}横线处填入下面那一条语句不会报错______A、public float getNum(){return 4.0f;}B、public void getNum(){}C、void getNum(double d) {}D、public double getNum(float d) { return 4.0f;}

16.interface A {double f(double x, double y);}class B implements A {public double f(double x, double y) { return x * y;}int g(int a, int b) { return a + b;}}public class Main {public static void main(String args]) { A a = new B();System.out.println(a.f(3, 5)); //【代码1】B b = (B) a;System.out.println(b.g(3, 5)); //【代码2】}}00interface A {double f(double x, double y);}class B implements A {public double f(double x, double y) { return x * y;}int g(int a, int b) { return a + b;}}public class Main {public static void main(String args]) { A a = new B();System.out.println(a.f(3, 5)); //【代码1】B b = (B) a;System.out.println(b.g(3, 5)); //【代码2】}} 请说出下面程序中【代码1】和【代码2】的输出结果，以空格隔开。

17.interface A { double f(double x,double y); } class B implements A { public double f(double x,double y) { return x*y; } int g(int a,int b) { return a+b; } } public class E { public static void main(String args[]) { A a = new B(); System.out.println(a.f(3,5)); //【代码1】 B b = (B)a; System.out.println(b.g(3,5)); //【代码2】 } }

18.请说出E类中【代码1】，【代码2】的输出结果。interface A { double f(double x,double y); }class B implements A { public double f(double x,double y) { return x*y; } int g(int a,int b) { return a+b; }}public class E {public static void main(String args[]) { A a = new B(); System.out.println(a.f(3,5)); //【代码1】 B b = (B)a; System.out.println(b.g(3,5)); //【代码2】 }}

19.请说出E类中【代码1】的输出结果。class A { double f(double x,double y) { return x+y; }}class B extends A { double f(int x,int y) { return x*y; }}public class E {public static void main(String args[]) { B b=new B(); System.out.println(b.f(3,5)); //【代码1】

20.下列选项中，（）代码替换程序中标注的【代码】，将导致编译错误。class A{public float getNum(){return 3.0f;}}public class B extends A{【代码】} 选项： A、public float getNum( ){return 4.0f;} B、 public void getNum( ){ } C、 public void getNum(double d){ } D、 public double getNum(float d){return 4.0d;}

21.下列选项中，（）代码替换源文件Com.java中的【代码】不会导致编译错误。class A {public float getNum() {return 3.0f;}}public class B extends A {【代码】} 选项： A、public float getNum(){return 4.0f;} B、 public void getNum(){ } C、 public void getNum(double d){ } D、 public double getNum(float d){return 4.0d;}

22.请在【代码】处填写正确的代码。interface A{ final static double PI=3.14; public default double area(int r){ return r*r*PI; } abstract double volume(int r,double h);}interface B{ public default double area(int r){ return r*r; }}public class C implements A,B { public double volume(int r,double h){ return area(r)*h; } public static void main(String[] args){ C c=new C(); System.out.println("柱体体积为："+c.volume(1,2.0)); } public double area(int r){ return 【代码】; //委托调用父接口A中的area()方法 }}