Integer函数

Integer.parseInt()函数：将字符串参数解析为带符号的十进制整数，返回由十进制参数表示的整数值。

简单点就是将String类型的数字，转换成int类型

public static void main(String[] args) {
        String s="120";
        int i=Integer.parseInt(s);
        System.out.println(i);//输出120
    }

这是parseInt函数的源码

public static int parseInt(String s, int radix)//radix默认是10
                throws NumberFormatException{
        if (s == null) {
            throw new NumberFormatException("null");
        }
        //大于2
        if (radix < Character.MIN_RADIX) {
            throw new NumberFormatException("radix " + radix +
                                            " less than Character.MIN_RADIX");
        }
        //小于36
        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;
    }

默认传的radix为10，就是10进制

校验传过来的数据只能为数字：

matches方法主要是返回是否匹配指定的字符串，如果匹配则为true,否则为false;

public static void main(String[] args) {
        String i="72";  //输出Yes
        // String i="ass";  输出No
        if(i.matches("[0-9]*")) {
            System.out.println("Yes");
        }else {
            System.out.println("No");
        }
    }