比较If else 和 try catch 的jvm指令

编码时过度关注某个点性能，有时候整体性能适得其反！关于if else 和 try catch 的性能争辩，看下其JVM指令，再结合各自的使用场景，自己慢慢理解。在此不做评论！

 

另外强调下java的Exception.class！

public class Exception extends Throwable{}

看下Throwable类的结构和设计有好处，便于理解堆栈信息为啥能从Thread的起点到异常点都能打印出来！

 

 

先上Java Code:

 

public class Test{

    public void viewException(){

         try{
            String a = "123_a_"+3;
         }catch(Exception e){
            System.out.println("exception");
         }

    }

    public void viewThrow(){

        try{

            int a = 1+888;
        }catch(Exception e){
             throw new RuntimeException(e);
        }
    }


    public int viewIfelse(int num){
        if(num==1){
           return 1;
        }else if(num==2){
           return 2;
        }else{
           return 0;
        }
    }

}

 

 

再看反编译的JVM 指令：

 

Compiled from "Test.java"
public class Test extends java.lang.Object{
public Test();
  Code:
   0:   aload_0
   1:   invokespecial   #1; //Method java/lang/Object."<init>":()V
   4:   return

public void viewException();
  Code:
   0:   ldc     #2; //String 123_a_3
   2:   astore_1
   3:   goto    7
   6:   astore_1
   7:   return
  Exception table:
   from   to  target type
     0     3     6   Class java/lang/Exception


public void viewThrow();
  Code:
   0:   sipush  889
   3:   istore_1
   4:   goto    17
   7:   astore_1
   8:   new     #4; //class java/lang/RuntimeException
   11:  dup
   12:  aload_1
   13:  invokespecial   #5; //Method java/lang/RuntimeException."<init>":(Ljava/lang/Throwable;)V
   16:  athrow
   17:  return
  Exception table:
   from   to  target type
     0     4     7   Class java/lang/Exception


public int viewIfelse(int);
  Code:
   0:   iload_1
   1:   iconst_1
   2:   if_icmpne       7
   5:   iconst_1
   6:   ireturn
   7:   iload_1
   8:   iconst_2
   9:   if_icmpne       14
   12:  iconst_2
   13:  ireturn
   14:  iconst_0
   15:  ireturn

}