如何判断一个字符串是否是数字？

1.用JAVA自带的函数

package com.luna.test;
public class IsNUmber {
	public static void main(String[] args) {
		String s1 = "10";
		String s2 = "-10";
		String s3 = "a10";
		String s4 = "10b";
		String s5 = "01";
		System.out.println(isNumerOrigin(s1));
		System.out.println(isNumerOrigin(s2));
		System.out.println(isNumerOrigin(s3));
		System.out.println(isNumerOrigin(s4));
		System.out.println(isNumerOrigin(s5));
	}
	
	public static boolean isNumerOrigin(String str) {
	    for (int i = 0; i < str.length(); i++) {
	        if (!Character.isDigit(str.charAt(i))) {
	            return false;
	        }
	    }
	    return true;
	}
}

输出结果：true，false，false，false，true。注意：这种方式不能用来判断负数。

2.用正则表达式

package com.luna.test;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class IsNUmber {
	public static void main(String[] args) {
		String s1 = "10";
		String s2 = "-10";
		String s3 = "a10";
		String s4 = "10b";
		String s5 = "01";
		System.out.println(isNumerRule(s1));
		System.out.println(isNumerRule(s2));
		System.out.println(isNumerRule(s3));
		System.out.println(isNumerRule(s4));
		System.out.println(isNumerRule(s5));
	}
	
	public static boolean isNumerRule(String str) {
        Pattern pattern = Pattern.compile("-?[0-9]+\\.?[0-9]*");
        Matcher isNum = pattern.matcher(str);
        if (!isNum.matches()) {
            return false;
        }
        return true;
    }
}

输出结果：true，true，false，false，true。适用于任何正负数字。

3.判断是否为整数(非严格数字判断)

/**
 * 判斷是否為整數
 * @param str
 * @return
 */
public static boolean isNumer(String str) {
    Pattern pattern = Pattern.compile("^[-\\+]?[\\d]*$");
    return pattern.matcher(str).matches();
}

/**
 * 判斷是否為正整數
 * @param str
 * @return
 */
public static boolean isNumerInteger(String str) {
    if (str != null && !"".equals(str.trim())) {
          return str.matches("^[0-9]*$");
    }
    return false;
}

/**
 * 判斷是否為正整數
 * @param str
 * @return
 */
public static boolean isNumericInt (String str) {
    Pattern pattern = Pattern.compile("[0-9]*");
    return pattern.matcher(str).matches();
}