変数が数値かどうかを判断するための Java メソッドの概要

public static boolean isNumeric(String str){
for (int i = 0; i < str.length(); i++){
   System.out.println(str.charAt(i));
   if (!Character.isDigit(str.charAt(i))){
    return false;
   }
}
return true;
}

public boolean isNumeric(String str){
   Pattern pattern = Pattern.compile("[0-9]*");
   Matcher isNum = pattern.matcher(str);
   if( !isNum.matches() ){
       return false;
   }
   return true;
}

org.apache.commons.lang.StringUtils;
boolean isNunicodeDigits=StringUtils.isNumeric("aaa123456789");
http://jakarta.apache.org/commons/lang/api-release/index.html下面的解释:
isNumeric
public static boolean isNumeric(String str)Checks if the String contains only unicode digits. A decimal point is not a unicode digit and returns false.
null will return false. An empty String ("") will return true.
StringUtils.isNumeric(null)   = false
StringUtils.isNumeric("")     = true
StringUtils.isNumeric(" ")   = false
StringUtils.isNumeric("123") = true
StringUtils.isNumeric("12 3") = false
StringUtils.isNumeric("ab2c") = false
StringUtils.isNumeric("12-3") = false
StringUtils.isNumeric("12.3") = false

Parameters:
str - the String to check, may be null
Returns:
true if only contains digits, and is non-null

import java.io.* ;
import java.util.* ;
public class Test{
public static void main(String [] args) throws Exception{
System.out.println("请输入数字:");
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
   String line=br.readLine();
    if(line.matches("\\d+"))     //正则表达式 详细见java.util.regex 类 Pattern
   System.out.println("数字");
   else
   System.out.println("非数字");
}
}

 public static boolean isNumeric0(String str){
  for(int i=str.length();--i>=0;){
   int chr=str.charAt(i);
   if(chr<48 || chr>57)
    return false;
  }
  return true;
 }

 public static boolean isNumeric3(String str){
  final String number = "0123456789";
  for(int i = 0;i
            if(number.indexOf(str.charAt(i)) == -1){  
             return false;  
            }  
  }  
  return true;
 }

 public static boolean isNumeric00(String str){
  try{
   Integer.parseInt(str);
   return true;
  }catch(NumberFormatException e){
   System.out.println("异常：\"" + str + "\"不是数字/整数...");
   return false;
  }
 }

 public static long parseLong(String s,int radix)  
         throws NumberFormatException  
 {  
    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");  
    }  
    long result = 0;  
    boolean negative = false;
    int i = 0,max = s.length();  
    long limit;  
    long multmin;  
    int digit;
    if(max > 0){  
     if(s.charAt(0) == &#39;-&#39;){  
      negative = true;  
      limit = Long.MIN_VALUE;
      i++;
     }else{
      limit = -Long.MAX_VALUE;
     }  
     multmin = limit / radix;
     if(i < max){  
      digit = Character.digit(s.charAt(i++),radix);  
      if(digit < 0){
            throw new NumberFormatException(s);  
      }else{  
            result = -digit;
      }  
     }  
     while(i < max){  
      // Accumulating negatively avoids surprises near MAX_VALUE
      digit = Character.digit(s.charAt(i++),radix);  
      if(digit < 0){  
       throw new NumberFormatException(s);  
      }  
      if(result < multmin){  
       throw new NumberFormatException(s);  
      }  
      result *= radix;  
      if(result < limit + digit){  
       throw new NumberFormatException(s);  
      }  
      result -= digit;  
    }  
    }else{  
     throw   new   NumberFormatException(s);  
    }  
    if(negative){  
     if(i > 1){  
      return result;
     }else{  
      throw new NumberFormatException(s);  
     }  
    }else{  
     return   -result;  
    }  
 }