public void calc(){
        int i = 1;
        i = i++;
        System.out.println(i);
    }

對應的字節(jié)碼指令如下：

calc:()V
000:    iconst_1                                {Lsample/HelloWorld;, .} | {}
001:    istore_1                                {Lsample/HelloWorld;, .} | {I}
002:    iload_1                                 {Lsample/HelloWorld;, I} | {}
003:    iinc 1 1                                {Lsample/HelloWorld;, I} | {I}
004:    istore_1                                {Lsample/HelloWorld;, I} | {I}
005:    getstatic System.out                    {Lsample/HelloWorld;, I} | {}
006:    iload_1                                 {Lsample/HelloWorld;, I} | {Ljava/io/PrintStream;}
007:    invokevirtual PrintStream.println       {Lsample/HelloWorld;, I} | {Ljava/io/PrintStream;, I}
008:    return                                  {Lsample/HelloWorld;, I} | {}

public void calc(){
        int i = 1;
        i = ++i;
        System.out.println(i);
    }


對應的字節(jié)碼指令如下：

calc:()V
000:    iconst_1                                {Lsample/HelloWorld;, .} | {}
001:    istore_1                                {Lsample/HelloWorld;, .} | {I}
002:    iinc 1 1                                {Lsample/HelloWorld;, I} | {}
003:    iload_1                                 {Lsample/HelloWorld;, I} | {}
004:    istore_1                                {Lsample/HelloWorld;, I} | {I}
005:    getstatic System.out                    {Lsample/HelloWorld;, I} | {}
006:    iload_1                                 {Lsample/HelloWorld;, I} | {Ljava/io/PrintStream;}
007:    invokevirtual PrintStream.println       {Lsample/HelloWorld;, I} | {Ljava/io/PrintStream;, I}
008:    return                                  {Lsample/HelloWorld;, I} | {}

iload

istore

image.png

iinc.png

指定包名厕鹃，統計方法耗時

//代碼

public void calc(){
        int i = 1;
        i = i++;
        System.out.println(i);
    }

//對應的字節(jié)碼指令如下
calc:()V
000:    iconst_1                                {Lsample/HelloWorld;, .} | {I}
001:    istore_1                                {Lsample/HelloWorld;, I} | {}
002:    iload_1                                 {Lsample/HelloWorld;, I} | {I} //把局部變量表索引為1位置的值   放到操作數棧中  （操作數棧頂元素的值為 1）
003:    iinc 1 1                                {Lsample/HelloWorld;, I} | {I} //把局部變量表索引為1位置的值加1  (局部變量表該位置的值 i=2)
//棧頂元素彈棧并把值（棧頂元素的值為1）存到局部變量表索引為1的位置（局部變量表索引為1位置的值由2變?yōu)?）
004:    istore_1                                {Lsample/HelloWorld;, I} | {}  
005:    getstatic System.out                    {Lsample/HelloWorld;, I} | {Ljava/io/PrintStream;} 
006:    iload_1                                 {Lsample/HelloWorld;, I} | {Ljava/io/PrintStream;, I}
007:    invokevirtual PrintStream.println       {Lsample/HelloWorld;, I} | {}
008:    return                                  

//代碼

public void calc(){
        int i = 1;
        i = ++i;
        System.out.println(i);
    }
//對應的字節(jié)碼指令如下
calc:()V
000:    iconst_1                                {Lsample/HelloWorld;, .} | {I}
001:    istore_1                                {Lsample/HelloWorld;, I} | {}  
002:    iinc 1 1                                {Lsample/HelloWorld;, I} | {} //把局部變量表索引為1位置的值加1 (i = 2)
003:    iload_1                                 {Lsample/HelloWorld;, I} | {I}//把局部變量表索引為1位置的值放到操作數棧中（棧頂元素值為2）
//棧頂元素彈棧并把值（棧頂元素的值為2）存到局部變量表索引為1的位置（局部變量表索引為1位置的值由1變?yōu)?）
004:    istore_1                                {Lsample/HelloWorld;, I} | {}
005:    getstatic System.out                    {Lsample/HelloWorld;, I} | {Ljava/io/PrintStream;}
006:    iload_1                                 {Lsample/HelloWorld;, I} | {Ljava/io/PrintStream;, I}
007:    invokevirtual PrintStream.println       {Lsample/HelloWorld;, I} | {}
008:    return