第四章 没啥好说的......
4.1
1 package ex0401;
2 //[4.1]写一个程序打印从1到100的值
3
4 public class PrintOneToHundred
5 {
6 public static void main(String[] args)
7 {
8 for(int i = 1; i <= 100; ++i)
9 System.out.print(i + " ");
10 }
11 }
4.1
4.2-4.3
1 package ex040203;
2 //[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
3 //[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).
4
5 import java.util.Random;
6
7 public class GetRandomInteger
8 {
9 public static void main(String[] args)
10 {
11 int i = 0;
12 Random rand = new Random();
13 int curr = rand.nextInt();
14 int prev = 0;
15 //[4.2]
16 while(++i < 25)
17 //[4.3]
18 //while(true)
19 {
20 prev = rand.nextInt();
21 System.out.print(curr + " ");
22 if(curr > prev)
23 System.out.print("greater than ");
24 else if(curr < prev)
25 System.out.print("less than ");
26 else
27 System.out.print("equals ");
28 curr = prev;
29 }
30 System.out.print(prev);
31 }
32 }
4.2-4.3
4.4
1 package ex0404;
2 //[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
3
4 public class GetPrime
5 {
6 public static void main(String[] args)
7 {
8 System.out.println(2);
9 for(int number = 3; number < 10000; number += 2)
10 {
11 int index;
12 for(index = 3; index < number ; index += 2)
13 {
14 if(number % index == 0)
15 break;
16 }
17 if(index * index > number)
18 System.out.println(number);
19 }
20 }
21 }
4.4
4.5
1 package ex0405;
2 //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
3
4 public class AnotherBitOperation
5 {
6 public static void main(String[] args)
7 {
8 int first = 0x2AA;
9 int second =0x133;
10
11 for(int i = 0; ((first >> i) & 0xFFFF) != 0; ++i)
12 System.out.print((first >> i ) & 1);
13 System.out.println("");
14 for(int i = 0; ((second >> i) & 0xFFFF) != 0; ++i)
15 System.out.print((second >> i ) & 1);
16 System.out.println("");
17 for(int i = 0; (((first & second) >> i) & 0xFFFF) != 0; ++i)
18 System.out.print(((first & second) >> i ) & 1);
19 System.out.println("");
20 for(int i = 0; (((first | second) >> i) & 0xFFFF) != 0; ++i)
21 System.out.print(((first | second) >> i ) & 1);
22 System.out.println("");
23 for(int i = 0; (((first ^ second) >> i) & 0xFFFF) != 0; ++i)
24 System.out.print(((first ^ second) >> i ) & 1);
25 System.out.println("");
26 }
27 }
4.5
4.7
1 package ex0407;
2 //[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
3
4 public class TestBreakAndReturn
5 {
6 public static void main(String[] args)
7 {
8 for(int i = 1; i <= 100; ++i)
9 {
10 if(i == 100)
11 return;
12 //break;
13 System.out.print(i + " ");
14 }
15 }
16 }
4.7
4.8
1 package ex0408;
2 //[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.
3 //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.
4
5 public class TestSwitch
6 {
7 public static void main(String[] args)
8 {
9 for(int i = 0; i < 3; ++i)
10 {
11 switch(i)
12 {
13 case 0:
14 System.out.println("Cat");//break;
15 case 1:
16 System.out.println("Dog");//break;
17 case 2:
18 System.out.println("Bird");//break;
19 default:
20 break;
21 }
22 }
23 }
24 }
4.8
4.9
1 package ex0409;
2 //[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.
3 //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.
4
5 class Fibonacci
6 {
7 private static final int FIRST = 1;
8 private static final int SECOND = 1;
9
10 public static void printFibonacci(int length)
11 {
12 if(length <= 0)
13 System.out.println("error!");
14 switch(length)
15 {
16 case 2:
17 System.out.println(FIRST);
18 case 1:
19 System.out.println(SECOND);break;
20 default:
21 {
22 int prevprev = FIRST;
23 int prev = SECOND;
24 int curr;
25 System.out.println(FIRST);
26 System.out.println(SECOND);
27 for(int i = 3; i <= length; ++i)
28 {
29 curr = prevprev + prev;
30 System.out.println(curr);
31 prevprev = prev;
32 prev = curr;
33 }
34 }
35 }
36 }
37 }
38 public class ShowFibonacci
39 {
40 public static void main(String[] args)
41 {
42 Fibonacci.printFibonacci(10);
43 }
44 }
4.9
时间： 2024-08-02 02:44:44