条件转移指令实战

快来打我* 2022-09-04 09:49 179阅读 0赞

# 一 ifeq 指令 #

## 1 代码 ##

public void compare1() {
        int a = 0;
        if (a != 0) {
            a = 10;
        } else {
            a = 20;
        }
    }

## 2 对应字节码 ##

> 0 iconst\_0
> 
> 1 istore\_1
> 
> 2 iload\_1
> 
> 3 ifeq 12 (+9)
> 
> 6 bipush 10
> 
> 8 istore\_1
> 
> 9 goto 15 (+6)
> 
> 12 bipush 20
> 
> 14 istore\_1
> 
> 15 return

# 二 ifnonnull #

## 1 代码 ##

public boolean compareNull(String str) {
        if (str == null) {
            return true;
        } else {
            return false;
        }
    }

## 2 对应字节码 ##

> 0 aload\_1
> 
> 1 ifnonnull 6 (+5)
> 
> 4 iconst\_1
> 
> 5 ireturn
> 
> 6 iconst\_0
> 
> 7 ireturn

# 三 结合比较指令 #

## 1 代码 ##

// 结合比较指令
    public void compare2() {
        float f1 = 9;
        float f2 = 10;
        System.out.println(f1 < f2); // true
    }

## 2 图解 ##

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70][]

# 四 int 和 long 进行比较 #

## 1 代码 ##

public void compare3() {
        int i1 = 10;
        long l1 = 20;
        System.out.println(i1 > l1);
    }

## 2 图解 ##

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70 1][]

# 五 两个 double 进行比较 #

## 1 代码 ##

public int compare4(double d) {
        if (d > 50.0) {
            return 1;
        } else {
            return -1;
        }
    }

## 2 字节码 ##

> 0 dload\_1
> 
> 1 ldc2\_w \#8 <50.0>
> 
> 4 dcmpl
> 
> 5 ifle 10 (+5)
> 
> 8 iconst\_1
> 
> 9 ireturn
> 
> 10 iconst\_m1
> 
> 11 ireturn

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70 1]: /images/20220829/6ec6a42381a24430b36192887eebd70c.png