Java练习题1（有答案）(13)

3、 When executing System.out.println(a2), the toString() method in the Object class is invoked.

4、 When executing System.out.println(a1), the toString() method in the A class is invoked.

答案 3 4 第 128题 What is the output of the following code: public class Test {

public static void main(String[] args) { Object o1 = new Object(); Object o2 = new Object();

System.out.print((o1 == o2) + \ } }

1、 false false 2、 true true

3、 false true 4、 true false 答案 1 第 129题 What is the output of the following code: public class Test {

public static void main(String[] args) {

String s1 = new String(\ String s2 = new String(\

System.out.print((s1 == s2) + \ } }

1、 false false 2、 true true 3、 false true

4、 true false 答案 3 第 130题 Analyze the following code. //

Program

1:

public class Test {

public static void main(String[] args) { Object a1 = new A(); Object a2 = new A();

System.out.println(a1.equals(a2)); } } class A { int x; public boolean equals(Object a) { return this.x == ((A)a)x; } } //

Program

2:

public class Test {

public static void main(String[] args) { Object a1 = new A(); Object a2 = new A();

System.out.println(a1.equals(a2)); } } class A { int x; public boolean equals(A a) { return this.x == a.x; } }

1、 Program 1 displays true and Program 2 displays true 2、 Program 1 displays false and Program 2 displays true 3、 Program 1 displays true and Program 2 displays false 4、 Program 1 displays false and Program 2

displays false 答案 3 第 131题 Analyze the following code. //

Program

1:

public class Test {

public static void main(String[] args) { Object a1 = new A();

Object a2 = new A();

System.out.println(a1.equals(a2)); } } class A { int x; public boolean equals(A a) { return this.x == a.x; } } //

Program

2:

public class Test {

public static void main(String[] args) { A a1 = new A(); A a2 = new A();

System.out.println(a1.equals(a2)); } } class A { int x; public boolean equals(A a) { return this.x == a.x; } }

1、 Program 1 displays true and Program 2 displays true 2、 Program 1 displays false and Program 2 displays true 3、 Program 1 displays true and Program 2 displays false 4、 Program 1 displays false and Program 2 displays false 答案 2 第 132题 Analyze the following code. //

Program

1

public class Test {

public static void main(String[] args) { Object a1 = new A(); Object a2 = new A();

System.out.println(((A)a1).equals((A)a2));