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！

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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！

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先上Java Code:

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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;        }    }}

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再看反编译的JVM 指令：

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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:   returnpublic 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/Exceptionpublic 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/Exceptionpublic 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}

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