第四章 沒啥好說的......
4.1
1 package ex0401;
2 //[4.1]寫一個程式列印從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 } 4.2-4.3
1 package ex040203;
2 //[4.2]寫一個程式,産生25個int類型的随機數.對于每一個随機值,使用if-else語句來講其分類為大于\小于,或等于緊随它産生的值
3 //[4.3]修改練習2,把代碼用一個while無限循環包括起來.然後運作它直至鍵盤中斷其運作(通常是通過按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 } 4.4
1 package ex0404;
2 //[4.4]寫一個程式,使用兩個嵌套的for循環和取餘操作符來探測和列印素數
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 } 4.5
1 package ex0405;
2 //重複練習[3.10],不要用Integer.toBinaryString()方法,而是用三元操作符合按位操作符來顯示二進制的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 } 4.7
1 package ex0407;
2 //[4.7]修改本章練習1,通過使用break關鍵詞,使得程式在列印到99時退出.然後嘗試用return達到相同目的
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 } 4.8
1 package ex0408;
2 //[4.8]寫一個switch開關語句,為每個case列印一個消息.然後把這個switch放進for循環來測試每個case.
3 //先讓每個case後面都有break,測試一下會怎麼樣;然後把break删除,看看會怎樣.
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 } 4.9
1 package ex0409;
2 //[4.9]一個斐波那契數列是由數字從第三個數字其都是前兩個數字的和.
3 //建立一個方法,接收一個整數參數,并顯示從第一個元素開始,總共有該參數指定的個數所構成的所有斐波那契數字.
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 }