Java中valueOf与parseInt方法比较

柔情只为你懂 2022-05-18 23:18 186阅读 0赞

文章转载：[Java中valueOf与parseInt方法比较][Java_valueOf_parseInt]

#### 描述 ####

来自JDK8官方文档，这里只比较参数为String的两个方法  
1.public static int parseInt(String s)

> Parses the string argument as a signed decimal integer. The characters in the string must all be decimal digits, except that the first character may be an ASCII minus sign ‘-’ (‘\\u002D’) to indicate a negative value or an ASCII plus sign ‘+’ (‘\\u002B’) to indicate a positive value. The resulting integer value is returned, exactly as if the argument and the radix 10 were given as arguments to the parseInt(java.lang.String, int) method.  
> Parameters:  
> s - a String containing the int representation to be parsed  
> Returns:  
> the integer value represented by the argument in decimal.  
> Throws:  
> NumberFormatException - if the string does not contain a parsable integer.

2.public static Integer valueOf(String s)

> Returns an Integer object holding the value of the specified String. The argument is interpreted as representing a signed decimal integer, exactly as if the argument were given to the parseInt(java.lang.String) method. The result is an Integer object that represents the integer value specified by the string.  
> In other words, this method returns an Integer object equal to the value of:  
> new Integer(Integer.parseInt(s))  
> Parameters:  
> s - the string to be parsed.  
> Returns:  
> an Integer object holding the value represented by the string argument.  
> Throws:  
> NumberFormatException - if the string cannot be parsed as an integer.

### 比较 ###

首先从返回类型可以看出parseInt返回的是基本类型int，而valueOf返回的是对象。再看valueOf的描述有

new Integer(Integer.parseInt(s))

可以大胆猜测valueOf的内部其实就是调用了parseInt方法。  
所以直接去找源码。

public static Integer valueOf(String s) throws NumberFormatException {
            return Integer.valueOf(parseInt(s, 10));
     }
     public static Integer valueOf(int i) {
        assert IntegerCache.high >= 127;
     if (i >= IntegerCache.low && i <= IntegerCache.high)
            return IntegerCache.cache[i + (-IntegerCache.low)];
        return new Integer(i);
     }
     public static int parseInt(String s) throws NumberFormatException {
        return parseInt(s,10);
     }

### 结语 ###

因为JDK5以后实现了自动拆装箱，因而两者的差别也不是特别大了，但是从效率上考虑，建议首先考虑parseInt方法。

[Java_valueOf_parseInt]: https://blog.csdn.net/polar_geass/article/details/78977492