Java中String与StringBuffered常见笔试题

1:需求：请设计一个方法，可以实现获取任意范围内的随机数。

package org.wests.InterviewQuestion;
/** * 1:需求：请设计一个方法，可以实现获取任意范围内的随机数。 * @author 代虎 * */
public class Question01 {
   

    public static void getRandom(double start,double end) {
        double random =  Math.random()*(end-start)+start;
        System.out.println(random);
    }

    public static void main(String[] args) {
        getRandom(10, 20);
        getRandom(0, 20);
        getRandom(100, 200);

    }
}

执行结果：
15.760649486959991
12.00285416285148
145.76020942009

2:下面代码执行的结果是:
public static void main(String[] args) {
        String s1 = new String("hello");
        String s2 = new String("hello");
        System.out.print(s1 == s2);
        System.out.print(",");
        System.out.println(s1.equals(s2));
    }
}

执行结果：false,true

3:下面代码执行的结果是:

public static void main(String arg[]) {
        StringBuffer a = new StringBuffer("A");
        StringBuffer b = new StringBuffer("B");
        operate(a, b);
        System.out.println(a + "," + b);
    }
    static void operate(StringBuffer x, StringBuffer y) {
        x.append(y);
        y = x;
    }

执行结果：AB,B

4、下列代码的执行结果是：

String str1 = "This is a test!";
    StringBuffer str2 =new StringBuffer( "This is a test!");
    str1 = str1+"Hi";
    str2.append("Hi");
    System.out.println("str1 == " + str1);
    System.out.println("str2 == " + str2);

执行结果：str1 == This is a test ! Hi
str2 == This is a test ! Hi

以下为反编译的结果：

// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://kpdus.tripod.com/jad.html
// Decompiler options: packimports(3) fieldsfirst ansi space 
// Source File Name: Question04.java

package org.wests.InterviewQuestion;

import java.io.PrintStream;

public class Question04
{

    public Question04()
    {
    }

    public static void main(String args[])
    {
        String str1 = "This is a test!";
        StringBuffer str2 = new StringBuffer("This is a test!");
        str1 = (new StringBuilder(String.valueOf(str1))).append("Hi").toString();
        str2.append("Hi");
        System.out.println((new StringBuilder("str1 == ")).append(str1).toString());
        System.out.println((new StringBuilder("str2 == ")).append(str2).toString());
    }
}

5:下面代码能最后打印的值是?

public class TestValue {
    private static int a;

    public static void main(String[] args) {
        modify(a);
        System.out.println(a);
    }

    public static void modify(int a) {
        a++;
    }

执行结果： 0