我的任务是创建一个计算给定向量大小的方法,然后使用javap -c
将其分解。
现在我必须展示幅度框架中每个局部变量对应于java中的哪些,以及字节码的哪些行对应于什么。
这是我制作的方法:
public class Vector {
/** Magnitude of vector
* Calculates the magnitude of the vector corresponding
* to the array a.
*
* @return magnitude
*/
public double magnitude(double[] a){
int n = a.length;
double sum = 1;
for (int i=0; i<n; i++){
sum = sum*a[i];
}
double magnitude = Math.sqrt(sum);
return magnitude;
}
}
这是使用javap -c
:
public class Vector {
public Vector();
Code:
0: aload_0
1: invokespecial #1 // Method java/lang/Object."<init>":()V
4: return
public double magnitude(double[]);
Code:
0: aload_1
1: arraylength
2: istore_2
3: dconst_1
4: dstore_3
5: iconst_0
6: istore 5
8: iload 5
10: iload_2
11: if_icmpge 27
14: dload_3
15: aload_1
16: iload 5
18: daload
19: dmul
20: dstore_3
21: iinc 5, 1
24: goto 8
27: dload_3
28: invokestatic #2 // Method java/lang/Math.sqrt:(D)D
31: dstore 5
33: dload 5
35: dreturn
}
答案 0 :(得分:4)
使用javap
标记运行-l
:
$ javap -c -l Vector
Compiled from "Vector.java"
public class Vector {
public Vector();
Code:
0: aload_0
1: invokespecial #1 // Method java/lang/Object."<init>":()V
4: return
LineNumberTable:
line 1: 0
public double magnitude(double[]);
Code:
0: aload_1
1: arraylength
2: istore_2
3: dconst_1
4: dstore_3
...
35: dreturn
LineNumberTable:
line 12: 0
line 14: 3
line 16: 5
line 18: 14
line 16: 21
line 22: 27
line 24: 33
}
例如,您可以看到说明3&amp; 4对应于第14行,其中1
被加载到索引为2的double
。