JAVA EXAM 1---25

JAVA 测试I http://www.jianshu.com/p/76b36d18844d
JAVA 测试II http://www.jianshu.com/p/e7f7d29b185a
JAVA 测试III http://www.jianshu.com/p/64d3495989a5

1

public class Test {
    public void main(){
        System.out.println("Hi");
    }

    public static void main (String [] args)
    {
        Test t=new Test();
        t.main();
    }
}

What will be happen if you compile and run above code?

1. It will not compile
2. It will not run
3. It will compile but will not run
4. It will output “Hi”

ANS: 4, 因为两个函数参数不同, 属于函数重载. 函数重载只考虑参数问题.

2

After execution of the code fragment below, what are the value of the variables x1, y1, and z1?

int x=10; int y =10; int z=10; int x1, y1, z1;
x1=++y;  //x1 = 11
y1=z++;  //y1 = 10
z1=z;    // z1 = 11

Choose the one below:

1. x1 = 10 , y1 = 10 and z1=10
2. x1 = 10, y1 = 11, and z1=10
3. x1=10, y1 = 10, and z1=11
4. x1=11, y1=10, and z1=11

选4

3

What will be the output?

public class Test {
    public int addTest(int x, int y) {
        x = x + 1;
        y = y + 1;
        int z = (x + y);
        return z;
    }

    public static void main(String[] args) {
        int x = 10;
        int y = 10;
        int z = 0;
        Test t = new Test();
        z = t.addTest(x, y);
        System.out.println("x =" + x + ",y =" + y + ",z = " + z);

    }
}

Choose the one below:

1. x=10, y=10, z=22
2. x=11, y=11, z=22
3. x=10, y=10, z=20
4. x=11, y=11, z=20

选1, 因为函数传的是☞, 不是地址.

4

What will be the output of the program.?
Assume that MyList class is declared in MyList.java
and ListManager class is declared in ListManager.java file.

public class Test {
    int size = 1;
    public static void main(String[] args)
    {
        Test list = new Test();
        list.size = 10;
        ListManager lm = new ListManager();
        lm.expandList(list);
        System.out.println("list.size = " + list.size);
    }
}  //end of MyList

public class ListManager {
    public void expandList(Test l)
    {
        l.size = l.size + 10;
    }
}

Choose the one below:

1. size=0
2. size=10
3. size=11
4. size=20

选4, 因为传的是类, 属于址传递.

5

If int x = -1 then which of the following expression results in a positive value in x?

1. x=x>>>32 // --> -1
2. x=x>>>5 // --> 134217727
3. x=x>>5 // ---> -1
4. x=~x // ---> 0

选2, 因为>>>是无符号右移,空位补0, -1的二进制是32个1, >>是有符号右移空位补符号位-1的符号位是1,4不正确, 题目是问正数.

6

6 . Which of the following lines of code would print “Equal” when you run it?

1. int x=1; float y=1.0F; if(x==y){ System.out.println("Equal");} //Equal
2. int x=1; Integer y= new Integer(1); if(x==y) {System.out.println("Equal");} // Equal
3. Integer x=new Integer(1); Integer y=new Intger(1); if(x==y){ System.out.println("Equal");} //不输出
4. String x="1"; String y="1"; if (x==y) { System.out.println("Equal");} //Equal

1 2 4都会输出 Equal,

7

Which of the following declarations are correct for the top level class?

1. public synchronized class MyTest extends Thread
2. private class MyTest extends Thread
3. public abstract class MyTest extends Thread
4. class MyTest extends Thread

选择3, 4

8

Consider the following lines of code:

public class Test {
    String x;

    public void testDemo(int n) {
        String y;
        if (n > 0) {
            y = "Hello";
        }
        System.out.println(x + y);
    }

    public static void main(String[] args) {
        Test test = new Test();
        test.testDemo(2);
    }
}  //end of MyList

1. It will produce compiler warning that variable y may not have been initialized
2. It will produce compiler warning that variable x may not have been initialized
3. It will output “Hello”
4. It will output “nullHello”

选2, 因为没有初始化y,编译失败

9

Consider that Parent and Child classes are defined in two different files as below:

class Parent {
    public Parent() {
        System.out.println("I am Parent");
    }
}

class Child extends Parent {
    public Child(int x) {
        System.out.println("I am Child");
    }

    public static void main(String[] args) {
        Child c = new Child(10);
    }
}

1. It will not compile.
2. It will compile successfully. It will output “I am Parent” and then “I am Child.”
3. It will compile successfully. It will output “I am Child” and then “I am Parent.”
4. It will compile successfully, but will not run.

这个题目有问题, Child和Parent首先得在一个包,第二Child类前得有public才能运行.
所以,要么编译成功,输出2, 要么编译成功但不会输出选4,

10

Consider following code:

import java.util.Vector;
public class Test {
    static int size;
    public expandList(int newSize) {
        ListExpander lexp = new ListExpander();
        Vector expandedList = lexp.expand();
        class ListExpander {
            public Vector expand() {
                Vector v = new Vector(this.size + newSize);
                return v;
            }
        }
    }
}

1. compiler error, “cannot refer inside an inner class to a static variable.”
2. compiler error, “cannot refer inside an inner class to to a non-final variable newSize defined in a different method.”
3. Both of the above
4. None of the above

如果expandList函数前有返回类型, 那么就选2 newSize需要声明为final类型, 如果没有,就选4

11

Consider following code:

public class Parent{
    public  int size =0;
    static class InnerClass{
        public void incrementParentSize(){
            XXX=XXX+10;
        }
    }
}

In above code, how can you access ‘size’ variable (of outer class Parent) inside innerclass at the place of ‘XXX’ ?

1. super.size
2. this.size
3. Parent.size
4. Can not access it`

选4, 静态内部类无法访问非静态成员, super是父类, this是当前类

12

Assume that Parent and Child classes are in different files:

public class Parent {
    public Parent(int x, int y)
    {
        System.out.println("Created Parent");
    }

}//end of Parent class

public class Child extends Parent {
    public Child(int x, int y) {
        super(x, y);
    }

    public Child(int x, int y, int z) {
        System.out.println("Creating child");
        this(x, y);
    }
    public static void main(String[] args) {
        Child c = new Child(1, 2, 3);
    }
}

What will happen if you try to compile and run above program?

1. It will compile successfully. It will output “Created Parent” and then “Creating child”
2. It will compile successfully. It will output “Creating child” and then “Created Parent”
3. It will not compile giving warning, “Explicit constructor invocation must be first statement in constructor.”
4. It will not compile giving warning, “Expression is not a valid block statement.”

一定不会编译的,选3, 4

13

Consider following code:

public class OuterClass{
    class InnerClass{
    }
    public void innerClassDemo(){
        //Explicit instance of InnerClass
    }
}

In above code, how can you explicitly create an instance of InnerClass?

1. InnerClass i=InnerClass();
2. InnerClass i=OuterClass.InnerClass();
3. InnerClass i=new OuterClass ().new InnerClass();
4. InnerClass i=new OuterClass.InnerClass();

前两个都没有new关键字, 选3, 4

14

Please select valid(有效) array declaration(s):

1. int x[20];
2. int []x=new int[20];
3. int [][] x=new int [20][];
4. int [][][] x=new int[20][20][20];
5. int [] x={1,2,3};

2, 3, 4, 5都正确, 1错误

15

Consider following code:

public class Test {
    protected void demo() throws NumberFormatException, ArrayIndexOutOfBoundsException {
        //something here
    }
    public void demo(String s) {
        //something here
    }
}//end of Test class

Please select true statement(s) for demo code?

1. It is an example of overloading method
2. It is an example of overriding method
3. Both of the above
4. None of the above

选1, 方法重载, overloading

16

For the following code, please consider that super class is defined in question #15:

class MyTest extends Test {
    private void demo() throws IndexOutOfBoundsException, ClassNotFoundException
    {
        //something here
    }
}//end of MyTest class

What will happen if you try to compile above code ?

1. It will compile successfully.
2. Compiler error: Exception java.lang.ClassNotFoundException in throws clause of void MyTest.demo() is not compatible with void Test.demo().
3. Compiler error: Cannot reduce visibility of the inherited method from Test.
4. Both B and C

选4, MyTest中的demo()无法覆盖Test中的demo()
正在尝试分配更低的访问权限; 以前为protected

17

Consider the following code:

public class Test {
    public void demo(String[] list) {
        try {
            String s = list[list.length + 1];
            System.out.println(s);
        } catch (ArrayIndexOutOfBoundsException e) {
            return;
        } finally {
            System.out.println("Finally here.");
        }
    }
    public static void main(String[] args) {
        Test t = new Test();
        String[] list = {"one","two"};
        t.demo(list);
        System.out.println("Done !");
    }
}//end of Test class

What happen if you try compile and run above code ?

1. It will not compile.
2. It will output “null” and then “Finally here.”
3. It will output “Done!”
4. It will output “Finally here” and then “Done!”

选4, 遇到catch里面return的时候,不执行,finally一定会执行!

18

Please consider following code:

public class Test{
    public static void demo(String s)
    {
      debug("In demo:"+s);
    }
    private void debug(String s){
        System.out.println(s);
    }
    public static void main(String [] args){
        Test.demo(“Hello”);
    }
}

What will happen if you try to compile and run above code ?

1. It will compile successfully, but will not run.
2. It will compile successfully, and outputs “In demo:Hello.”
3. It will not compile with error message “Can not make a static reference to the instance method named.”
4. None of the above

选3, 静态方法不能调用非静态方法

19

Consider the following code:

/**
 * File Drawable.java
 */

public interface Drawable {

    public void draw();

    public void fill();

} /**
 * End of file Drawable.java
 */

/** File Circle.java */
public class Circle implements Drawable {
    int center=0;
    public void draw(){
        System.out.println(“Drawing circle”);
    }
    public static void main(String [] args){
        Circle c=new Circle();
        c.draw()
    }
} /** End of file Circle.java */

If you attempt to compile and run Circle class what will be output?

1. It will compile successfully, and outputs “Drawing circle.”
2. It will not compile, and reports error: “class Circle must implement inherited abstract method void Drawable.fill.”
3. It will not compile, and reports error: “Method Drawable.fill requires a body instead of a semicolon.”
4. None of the above

选2, 因为只实现了接口的一个方法.

20

What will be the output?

int x=2; int y=3; int z=4;
if(x>2){
    System.out.println(“Tested x”);
}if(y<3){
   System.out.println(“Tested y”);
}if (z<=3){
   System.out.println(“Tested z”);
}

Choose the one below:

1. Tested x.
2. Tested y.
3. Tested z.
4. None of the above.

选4

21

Consider the following code:

for(int i=0;i<2;i++)
{
    for(int j=i;j<3; j++)
    {
        if (i==j)
        {
            continue;
        }
        System.out.println("i="+i+" j="+j);
    }
}

Which lines would be part of the output?

1. i = 0 j = 1
2. i = 0 j = 2
3. i = 1 j = 2
4. None of the above

选1 2 3,

22

Consider the following code:

int j=0;
for( int i=0;i<2;i++)
{
    for (j=i; j<3; j++)
    {
        continue;
    }
    System.out.println(“i = “+i+” j = “+j);
}

Which lines would be part of the output?

1. i = 0 j = 0
2. i = 1 j = 1
3. i = 0 j = 3
4. i = 1 j =3

选3 4

23

Consider the following code:

int i=0; int j=0;
for( i=0;i<2;i++)
{
    for (j=i; j<3; j++)
    {
        break;
    }
    System.out.println("i = "+i+" j = "+j);
}
```
Which **lines** would be part of the output?
1. i = 0 j = 0
2. i = 1 j = 1
3. i = 0 j = 3
4. i = 1 j = 3
> 选1  2

#### 24
Consider the following code:
```
int i, j=0;
outer:
for( i=0;i<2;i++)
{
    for (j=i; j<3; j++)
    {
        continue outer;
    }
  System.out.println("i = "+i+" j = "+j);
}
```
Which lines would be part of the output?
1. i = 0 j = 0
2. i = 1 j = 1
3. i = 0 j = 3
4. None of the above
> 选4, 什么都输出, 这里是 java label标号的用法

#### 25
Consider the following code:
```
int i, j=0;
for( i=0;i<2;i++)
{
    inner:
    for(j=i; j<3; j++)
    {
        break inner;
    }
    System.out.println("i = "+i+" j = "+j);
}
```
Which **lines** would be part of the output?
1. i = 0 j = 0
2. i = 1 j = 1
3. i = 0 j = 3
4. None of the above
> 选 1 2,