string转成integer

T_Mac|mumu 2020-10-27 04:40:54

不能使用Integer.parseInt()

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冰思雨 2020-11-05

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Integer integer = new Integer(“123”); int i = Integer.parseInt(“123”);

Python小叮当 2020-11-03

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引用 5 楼 Amin已经存在了的回复:

[quote=引用 1 楼程序杂谈的回复:][quote=引用楼主程序杂谈的回复:]不能使用Integer.parseInt()

比如说将String a="123"; 变成 inteager 123[/quote] Integer.parseInt（）返回值类型是int类型 Integer.valueOf（）返回值类型是Integer类型[/quote] 正解

Python小叮当 2020-11-03

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引用 5 楼 Amin已经存在了的回复:

[quote=引用 1 楼程序杂谈的回复:][quote=引用楼主程序杂谈的回复:]不能使用Integer.parseInt()

比如说将String a="123"; 变成 inteager 123[/quote] Integer.parseInt（）返回值类型是int类型 Integer.valueOf（）返回值类型是Integer类型[/quote] 官网api

https://docs.oracle.com/javase/8/docs/api/

宾灬 2020-10-30

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int str_to_num(char * str){
    size_t len = strlen(str);
    if(len == 0){
        return 0;
    }
    int num = 0;
    size_t index = 0;
    int flag = 1;
    if(str[0] == '-'){
        index = 1;
        flag = 0;
    }
    while (index < len){
        num *= 10;
        if(str[index] < '0' || str[index] > '9'){
            printf("有非法字符\n");
            exit(1);
        }
        num += (int)(str[index] - '0');
        index++;
    }
    return flag ? num :  -num;
}

brick mover 2020-10-30

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org.apache.commons.lang.math.NumberUtils#toInt(java.lang.String) 试下这个 commons-lang jar包下的

wujiuqier 2020-10-30

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new BigDecimal("222").intValue()

new Double("222").intValue()

new Float("222").intValue()

new Long("222").intValue()

或者直接上JDK源码

public static int parseInt(String s, int radix)
                throws NumberFormatException
    {
        /*
         * WARNING: This method may be invoked early during VM initialization
         * before IntegerCache is initialized. Care must be taken to not use
         * the valueOf method.
         */

        if (s == null) {
            throw new NumberFormatException("null");
        }

        if (radix < Character.MIN_RADIX) {
            throw new NumberFormatException("radix " + radix +
                                            " less than Character.MIN_RADIX");
        }

        if (radix > Character.MAX_RADIX) {
            throw new NumberFormatException("radix " + radix +
                                            " greater than Character.MAX_RADIX");
        }

        int result = 0;
        boolean negative = false;
        int i = 0, len = s.length();
        int limit = -Integer.MAX_VALUE;
        int multmin;
        int digit;

        if (len > 0) {
            char firstChar = s.charAt(0);
            if (firstChar < '0') { // Possible leading "+" or "-"
                if (firstChar == '-') {
                    negative = true;
                    limit = Integer.MIN_VALUE;
                } else if (firstChar != '+')
                    throw NumberFormatException.forInputString(s);

                if (len == 1) // Cannot have lone "+" or "-"
                    throw NumberFormatException.forInputString(s);
                i++;
            }
            multmin = limit / radix;
            while (i < len) {
                // Accumulating negatively avoids surprises near MAX_VALUE
                digit = Character.digit(s.charAt(i++),radix);
                if (digit < 0) {
                    throw NumberFormatException.forInputString(s);
                }
                if (result < multmin) {
                    throw NumberFormatException.forInputString(s);
                }
                result *= radix;
                if (result < limit + digit) {
                    throw NumberFormatException.forInputString(s);
                }
                result -= digit;
            }
        } else {
            throw NumberFormatException.forInputString(s);
        }
        return negative ? result : -result;
    }