Java练习题1（有答案）(12)

\ } } class B extends A { public B() { System.out.println(

\ } } public class C {

public static void main(String[] args) { B b = new B(); } }

1、 Nothing displayed

2、 \

3、 \is invoked\

4、 \is invoked\

5、 \default constructor of A is invoked\ 答案 3 第 126题 Analyze the following code: public class Test { public static void main(String[] args) { B b = new B(); b.m(5); System.out.println(\ } } class A { int i; public void m(int i) { this.i = i;

} } class B extends A { public void m(String s) { } }

1、 The program has a compilation error, because m is overridden with a different signature in B.

2、 The program has a compilation error, because b.m(5) cannot be invoked since the method m(int) is hidden in B.

3、 The program has a runtime error on b.i, because i is not accessible from b. 4、 The method m is not overridden in B. B inherits the method m from A and defines an overloaded method m in B.

答案 4 第 127题 Analyze the following code:

public class Test {

public static void main(String[] args) { Object a1 = new A(); Object a2 = new Object(); System.out.println(a1); System.out.println(a2); } } class A { int x; public String toString() { return \ } }

1、 The program cannot be compiled, because System.out.println(a1) is wrong and it should be replaced by System.out.println(a1.toString()); 2、 When executing System.out.println(a1), the toString() method in the Object class is invoked.