2018-07-02|2018-07-02 通过jvm编译指令，来解析i++与++i运算过程的区别 2018-07-02通过jvm编译指令，来解

通过jvm编译指令，来解析为何i++与++i运算过程的区别
i++

public void testFun(){ int y = 13; int x = y++; }

【2018-07-02|2018-07-02 通过jvm编译指令，来解析i++与++i运算过程的区别】对应指令结构

public void testFun(); descriptor: ()V flags: (0x0001) ACC_PUBLIC Code: stack=1, locals=3, args_size=1 0: bipush13 2: istore_1 3: iload_1 4: iinc1, 1 7: istore_2 8: return LineNumberTable: line 7: 0 line 8: 3 line 9: 8

++i

public void testFun(){ int y = 13; int x = ++y; }

public void testFun(); descriptor: ()V flags: (0x0001) ACC_PUBLIC Code: stack=1, locals=3, args_size=1 0: bipush13 2: istore_1 3: iinc1, 1 6: iload_1 7: istore_2 8: return LineNumberTable: line 7: 0 line 8: 3 line 9: 8

分析

i++ 3: iload_1//从局部变量表的slot_1位置加载变量到栈帧中 4: iinc1, 1 // 对slot_1位置的变量进行+1操作 7: istore_2// 将栈顶的值保存到slot_2，即对应代码应该是变量x ++i 3: iinc1, 1// 对slot_1的变量y进行+1操作 6: iload_1// 从slot_1加载变量y到栈帧,此时加载的Y的值已经被+1了 7: istore_2// 将帧栈的值，保存到局部变量表slot_2即变量x

通过上面的操作即可明显的看到i++与++i在指令的运算顺序的区别
Note: