【TIJ4】第四章全部习题

第四章 没啥好说的......

4.1

package ex0401;
//[4.1]写一个程序打印从1到100的值

public class PrintOneToHundred 
{
    public static void main(String[] args)
    {
        for(int i = 1; i <= 100; ++i)
            System.out.print(i + " ");
    }
}

4.2-4.3

package ex040203;
//[4.2]写一个程序,产生25个int类型的随机数.对于每一个随机值,使用if-else语句来讲其分类为大于小于,或等于紧随它产生的值
//[4.3]修改练习2,把代码用一个while无限循环包括起来.然后运行它直至键盘中断其运行(通常是通过按Ctrl+C).

import java.util.Random;

public class GetRandomInteger 
{
    public static void main(String[] args)
    {
        int i = 0;
        Random rand = new Random();
        int curr = rand.nextInt();
        int prev = 0;
        //[4.2]
        while(++i < 25)
        //[4.3]
        //while(true)
        {
            prev = rand.nextInt();
            System.out.print(curr + " ");
            if(curr > prev)
                System.out.print("greater than ");
            else if(curr < prev)
                System.out.print("less than ");
            else
                System.out.print("equals ");
            curr = prev;
        }
        System.out.print(prev);
    }
}

4.4

package ex0404;
//[4.4]写一个程序,使用两个嵌套的for循环和取余操作符来探测和打印素数

public class GetPrime 
{
    public static void main(String[] args)
    {
        System.out.println(2);
        for(int number = 3; number < 10000; number += 2)
        {
            int index;
            for(index = 3; index < number ; index += 2)
            {
                if(number % index == 0)
                    break;
            }
            if(index * index > number)
                System.out.println(number);
        }
    }
}

4.5

package ex0405;
//重复练习[3.10],不要用Integer.toBinaryString()方法,而是用三元操作符合按位操作符来显示二进制的1和0

public class AnotherBitOperation 
{
    public static void main(String[] args)
    {
        int first = 0x2AA;
        int second =0x133;
        
        for(int i = 0; ((first >> i) & 0xFFFF) != 0; ++i)
            System.out.print((first >> i ) & 1);
        System.out.println("");
        for(int i = 0; ((second >> i) & 0xFFFF) != 0; ++i)
            System.out.print((second >> i ) & 1);
        System.out.println("");
        for(int i = 0; (((first & second) >> i) & 0xFFFF) != 0; ++i)
            System.out.print(((first & second) >> i ) & 1);
        System.out.println("");
        for(int i = 0; (((first | second) >> i) & 0xFFFF) != 0; ++i)
            System.out.print(((first | second) >> i ) & 1);
        System.out.println("");
        for(int i = 0; (((first ^ second) >> i) & 0xFFFF) != 0; ++i)
            System.out.print(((first ^ second) >> i ) & 1);
        System.out.println("");
    }
}

4.7

package ex0407;
//[4.7]修改本章练习1,通过使用break关键词,使得程序在打印到99时退出.然后尝试用return达到相同目的

public class TestBreakAndReturn 
{
    public static void main(String[] args)
    {
        for(int i = 1; i <= 100; ++i)
        {
            if(i == 100)
                return;
                //break;
            System.out.print(i + " ");
        }
    }
}

4.8

package ex0408;
//[4.8]写一个switch开关语句,为每个case打印一个消息.然后把这个switch放进for循环来测试每个case.
//先让每个case后面都有break,测试一下会怎么样;然后把break删除,看看会怎样.

public class TestSwitch 
{
    public static void main(String[] args)
    {
        for(int i = 0; i < 3; ++i)
        {
            switch(i)
            {
            case 0:
                System.out.println("Cat");//break;
            case 1:
                System.out.println("Dog");//break;
            case 2:
                System.out.println("Bird");//break;
            default:
                break;
            }
        }
    }
}

4.9

package ex0409;
//[4.9]一个斐波那契数列是由数字从第三个数字其都是前两个数字的和.
//创建一个方法,接收一个整数参数,并显示从第一个元素开始,总共有该参数指定的个数所构成的所有斐波那契数字.

class Fibonacci
{
    private static final int FIRST = 1;
    private static final int SECOND = 1;

    public static void printFibonacci(int length)
    {
        if(length <= 0)
            System.out.println("error!");
        switch(length)
        {
        case 2:
            System.out.println(FIRST);
        case 1:
            System.out.println(SECOND);break;
        default:
        {
            int prevprev = FIRST;
            int prev = SECOND;
            int curr;
            System.out.println(FIRST);
            System.out.println(SECOND);
            for(int i = 3; i <= length; ++i)
            {
                curr = prevprev + prev;
                System.out.println(curr);
                prevprev = prev;
                prev = curr;
            }
        }
        }
    }
}
public class ShowFibonacci 
{
    public static void main(String[] args)
    {
        Fibonacci.printFibonacci(10);
    }
}