【Java高频面试题】--Java运算执行流程分析

古城微笑少年丶 2023-03-13 05:12 25阅读 0赞

## 1. Java高频面试题（一）-- Java运算执行流程分析 ##

public static void main(String[] args) { 
            int i=1;
    
            i=i++;
    
            int j=i++;
    
            int k=i+++i*i++;
    
            System.out.println("i="+i);
            System.out.println("j="+j);
            System.out.println("k="+k);
        }

相应字节码：

// access flags 0x9
      public static main([Ljava/lang/String;)V
       L0
        LINENUMBER 13 L0
        ICONST_1
        ISTORE 1
       L1
        LINENUMBER 15 L1
        ILOAD 1
        IINC 1 1
        ISTORE 1
       L2
        LINENUMBER 17 L2
        ILOAD 1
        IINC 1 1
        ISTORE 2
       L3
        LINENUMBER 19 L3
        ILOAD 1
        IINC 1 1
        ILOAD 1
        ILOAD 1
        IINC 1 1
        IMUL
        IADD
        ISTORE 3
       L4
        LINENUMBER 21 L4
        GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
        NEW java/lang/StringBuilder
        DUP
        INVOKESPECIAL java/lang/StringBuilder.<init> ()V
        LDC "i="
        INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
        ILOAD 1
        INVOKEVIRTUAL java/lang/StringBuilder.append (I)Ljava/lang/StringBuilder;
        INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String;
        INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
       L5
        LINENUMBER 22 L5
        GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
        NEW java/lang/StringBuilder
        DUP
        INVOKESPECIAL java/lang/StringBuilder.<init> ()V
        LDC "j="
        INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
        ILOAD 2
        INVOKEVIRTUAL java/lang/StringBuilder.append (I)Ljava/lang/StringBuilder;
        INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String;
        INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
       L6
        LINENUMBER 23 L6
        GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
        NEW java/lang/StringBuilder
        DUP
        INVOKESPECIAL java/lang/StringBuilder.<init> ()V
        LDC "k="
        INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)Ljava/lang/StringBuilder;
        ILOAD 3
        INVOKEVIRTUAL java/lang/StringBuilder.append (I)Ljava/lang/StringBuilder;
        INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String;
        INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
       L7
        LINENUMBER 24 L7
        RETURN
       L8
        LOCALVARIABLE args [Ljava/lang/String; L0 L8 0
        LOCALVARIABLE i I L1 L8 1
        LOCALVARIABLE j I L3 L8 2
        LOCALVARIABLE k I L4 L8 3
        MAXSTACK = 3
        MAXLOCALS = 4
    }

执行结果：  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQzMTk5MDE2_size_16_color_FFFFFF_t_70][]

*  `i=i++;执行过程分析`  
    ![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQzMTk5MDE2_size_16_color_FFFFFF_t_70 1][]
 *  `int j=i++;执行过程分析：`  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQzMTk5MDE2_size_16_color_FFFFFF_t_70 2]
 *  `int k=i+++i*i++;`  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQzMTk5MDE2_size_16_color_FFFFFF_t_70 3]

### 小结 ###

*  赋值=，最后计算。
 *  =右边的从左到右依次加载值依次压入操作数栈。
 *  实际先算那个，看运算符的优先级。
 *  自增、自减操作都是直接修改变量的值，不经过操作数栈。
 *  最后的赋值之前，临时结果也是存储在操作数栈中的。

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