Determine whether a string is a number in java

java中判断字符串是否是数字的方法如下：

1、用Java自带的方法

Java中有一个Character.isDig(char ch)

    public class CheckStrIsNum {   
        public static void main(String[] args) {     
            double aa = -192322.1212;    
            String a = "-192322.1212";  
            String b = "-192322a1212";     
            String c = "Java";  
            String d = "5";    
            /** 判断是否全为数字 */                     
            System.out.println(checkStrIsNum01(Double.toString(aa)));        
            System.out.println(checkStrIsNum01(a));        
            System.out.println(checkStrIsNum01(b));        
            System.out.println(checkStrIsNum01(c));        
            System.out.println(checkStrIsNum01(d)); 
        }
        
        /**
         * 利用Java的character.isDigit方法进行处理
         */
        public static boolean checkStrIsNum01(String str) {    
            for (int i = 0; i <p>显然b应该返回false才对，但是却返回true，而"5"应该返回true，也是结果错误。由此可见，这个结果，并不完美。</p><p><strong>2、利用正则表达式来判断</strong></p><p>利用正则表达式来-?[0-9]+(\\.[0-9]+)?来做判断字符串是否为数字。<br>如果传入的数据有很多位，那么使用double会导致精度丢失，这个时候就要用BigDecimal来进行转换。</p><pre class="brush:php;toolbar:false">    public class CheckStrIsNum {   
        public static void main(String[] args) {     
            double aa = -192322.1212;    
            String a = "-192322.1212";  
            String b = "-192322a1212";     
            String c = "Java";  
            String d = "5";    
            /** 判断是否全为数字 */                     
            System.out.println(checkStrIsNum02(Double.toString(aa)));        
            System.out.println(checkStrIsNum02(a));        
            System.out.println(checkStrIsNum02(b));        
            System.out.println(checkStrIsNum02(c));        
            System.out.println(checkStrIsNum02(d)); 
        }
        
        private static Pattern NUMBER_PATTERN = Pattern.compile("-?[0-9]+(\\.[0-9]+)?");
        /** 
         * 利用正则表达式来判断字符串是否为数字 
         */
         public static boolean checkStrIsNum02(String str) { 
            String bigStr; 
            try {      
                /** 先将str转成BigDecimal，然后在转成String */
                bigStr = new BigDecimal(str).toString(); 
            } catch (Exception e) { 
                /** 如果转换数字失败，说明该str并非全部为数字 */
                return false; 
            } 
            Matcher isNum = NUMBER_PATTERN.matcher(str); 
            if (!isNum.matches()) {    
                return false; 
            }  
            return true;
        }
    }

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