try..catch..到底影响性能吗?java
随便写一个简单的程序bash
public class Test {
public static void main(String[] args) {
int a = 0,b=2;
try {
a = b/0;
}catch (Exception e){
a = 1;
}
}
}
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看一下字节码指令过程:jvm
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: (0x0009) ACC_PUBLIC, ACC_STATIC
Code:
stack=2, locals=4, args_size=1
0: iconst_0 push 0
1: istore_1 pop并保存到局部变量1
2: iconst_2 push 2
3: istore_2 pop并保存到局部变量2
4: iload_2 从局部变量里拿出并push
5: iconst_0 push 0
6: idiv 栈顶两数相除
7: istore_1
8: goto 14
11: astore_3
12: iconst_1
13: istore_1
14: return
Exception table:
from to target type
4 8 11 Class java/lang/Exception
LineNumberTable:
line 8: 0
line 10: 4
line 13: 8
line 11: 11
line 12: 12
line 14: 14
LocalVariableTable:
Start Length Slot Name Signature
12 2 3 e Ljava/lang/Exception;
0 15 0 args [Ljava/lang/String;
2 13 1 a I
4 11 2 b I
StackMapTable: number_of_entries = 2
frame_type = 255 /* full_frame */
offset_delta = 11
locals = [ class "[Ljava/lang/String;", int, int ]
stack = [ class java/lang/Exception ]
frame_type = 2 /* same */
}
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能够看到有个异常表:性能
Exception table:
from to target type
4 8 11 Class java/lang/Exception
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from
表示try catch
的开始地址 to
表示try catch
的结束地址 target
表示异常的处理起始位 type
表示异常类名称测试
代码运行时出错时,会先判断出错位置是否在from - to
的范围,若是是,则从target
标志位往下执行,若是没有出错,直接goto
到return
。能够看出,若是代码不出错的话,性能几乎是不受影响的,和正常的代码执行是同样的。ui
那异常处理耗时是什么个概念呢?spa
public class Test {
public static void main(String[] args) {
int a = 0,b=2;
long startTime = System.nanoTime();
for (int i = 10; i>0;i--){
try {
a = b/i;
}catch (Exception e){
a = 1;
}finally {
}
}
long runTime = System.nanoTime()-startTime;
System.out.println(runTime);
}
}
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我只须要把i>0
改为i>=0
,程序遍会进行一次异常处理,由于除数不能为0.code
我在修改以前(无异常运行),运行的结果是1133
修改以后(会出现除数为0异常),运行结果是44177
ip
固然,这个结果和cpu的算力有关,屡次运行结果相差无几。资源
因此,能够看出一旦程序进入到catch里,是很是耗资源的。
那try catch 在for循环外面或者里面,哪一个更好呢?
public class Test {
public static void main(String[] args) {
int a = 0,b=2;
long startTime = System.nanoTime();
try {
for (int i = 10; i>=0;i--){
a = b/i;
}
}catch (Exception e){
a = 1;
}finally {
long runTime = System.nanoTime()-startTime;
System.out.println(runTime);
}
}
}
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运行屡次的控制台输出:
46820 48708 54749 47953 46820 45310
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public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: (0x0009) ACC_PUBLIC, ACC_STATIC
Code:
stack=2, locals=5, args_size=1
0: iconst_0
1: istore_1
2: iconst_2
3: istore_2
4: bipush 10
6: istore_3
7: iload_3
8: iflt 21
11: iload_2
12: iload_3
13: idiv
14: istore_1
15: iinc 3, -1
18: goto 7
21: goto 35
24: astore_3
25: iconst_1
26: istore_1
27: goto 35
30: astore 4
32: aload 4
34: athrow
35: return
Exception table:
from to target type
4 21 24 Class java/lang/Exception
4 21 30 any
24 27 30 any
30 32 30 any
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public class Test {
public static void main(String[] args) {
int a = 0,b=2;
long startTime = System.nanoTime();
for (int i = 10; i>=0;i--){
try {
a = b/i;
}catch (Exception e){
a = 1;
}finally {
}
}
long runTime = System.nanoTime()-startTime;
System.out.println(runTime);
}
}
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控制台打印:
42289 47953 49463 45688 45310
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public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: (0x0009) ACC_PUBLIC, ACC_STATIC
Code:
stack=2, locals=6, args_size=1
0: iconst_0
1: istore_1
2: iconst_2
3: istore_2
4: bipush 10
6: istore_3
7: iload_3
8: iflt 36
11: iload_2
12: iload_3
13: idiv
14: istore_1
15: goto 30
18: astore 4
20: iconst_1
21: istore_1
22: goto 30
25: astore 5
27: aload 5
29: athrow
30: iinc 3, -1
33: goto 7
36: return
Exception table:
from to target type
11 15 18 Class java/lang/Exception
11 15 25 any
18 22 25 any
25 27 25 any
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综合实验三和实验四,咱们发现不管从运行时长仍是从字节码指令的角度看,它两的性能能够说是同样的。并无你感受到的for循环里放try代码会冗余、资源消耗加倍的问题。
可是从运行逻辑来看,两个是有点不一样的,实验三中,由于for在try catch里,因此jvm在编译的时候,把异常处理放在for循环后面才进行。即:第24-27行
;实验四中,异常处理是在for循环内部的,即:第18-22行
。大同小异。
以上仅我的测试观点,若是有误请在下方留言,谢谢!