【Java语言】while与for执行效率对比
/blog/1005821
测试环境(虚拟机版本): sun jdk build 1.6.0_22-b04
测试程序
Java代码
1./**
2. * Copyright (c) 2011 Trusted Software and Mobile Computing(TSMC)
3. * All rights reserved.
4. * Author: Jarg Yee
5. * /
6. */
7. import java.util.*;
8./*
9. * 【Java语言】while,for执行效率对比
10. */
11.public class WhileFor
12.{
13. public static void main(String[] args)
14. {
15. System.out.println(whileTest());
16. System.out.println(forTest());
17.
18. }
19.
20. /** while测试 */
21. public static long whileTest()
22. {
23. int num = Integer.MAX_VALUE; // 迭代次数
24. long sum = 0; // 保存加法结果
25.
26. while((num--)>0)
27. {
28. sum = sum + num;
29. }
30.
31. return sum;
32. }
33.
34. /** for测试 */
35. public static long forTest()
36. {
37. int num=Integer.MAX_VALUE; // 迭代次数
38. long sum = 0; // 保存加法结果
39.
40. for(;(num--)>0;)
41. {
42. sum = sum + num;
43. }
44.
45. return sum;
46. }
47.}
class文件反编译指令
---------- Java反编译----------
Class文件反编译指令代码
piled from "WhileFor.java"
2.public class WhileFor extends ng.Object{
3.public WhileFor();
4. Code:
5. 0: aload_0
6. 1: invokespecial #1; //Method java/lang/Object."":()V
7. 4: return
8.
9. LineNumberTable:
10. line 11: 0
11.
12.
13.
14.public static void main(ng.String[]);
15. Code:
16. 0: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
17. 3: invokestatic #3; //Method whileTest:()J
18. 6: invokevirtual #4; //Method java/io/PrintStream.println:(J)V
19. 9: getstatic #2; //Field java/lang/System.out:Ljava/io/PrintStream;
20. 12: invokestatic #5; //Method forTest:()J
21. 15: invokevirtual #4; //Method java/io/PrintStream.println:(J)V
22. 18: return
23.
24. LineNumberTable:
25. line 15: 0
26. line 16: 9
27. line 18: 18
28.
29.
30.
31.public static long whileTest();
32. Code:
33. 0: ldc #6; //int 2147483647
34. 2: istore_0
35. 3: lconst_0
36. 4: lstore_1
37. 5: iload_0
38. 6: iinc 0, -1
39. 9: ifle 20
40. 12: lload_1
41. 13: iload_0
42. 14: i2l
43. 15: ladd
44. 16: lstore_1
45. 17: goto 5
46. 20: lload_1
47. 21: lreturn
48.
49. LineNumberTable:
50. line 23: 0
51. line 24: 3
52. line 26: 5
53. line 28: 12
54. line 31: 20
55.
56.
57.
58.public static long forTest();
59. Code:
60. 0: ldc #6; //int 2147483647
61. 2: istore_0
62. 3: lconst_0
63. 4: lstore_1
64. 5: iload_0
65. 6: iinc 0, -1
66. 9: ifle 20
