方法：

	/**
	 * check a string whether is numeric or not 
	 * @param String str 
	 * @return boolean true or false
	 */
	public static boolean is_numeric(String str) {
		try {
			Double d= Double.valueOf(str);
		} catch (java.lang.Exception e) {
			return false;
		}
		return true;
	}

测试代码：

public class Test {

	/**
	 * test the is_numeric method
	 * @param args 
	 */
	public static void main(String[] args) { 
		
		String s = "123.123";
		if (is_numeric(s)) {
			System.out.println(s+" is numeric");
		} else {
			System.out.println(s+" not numeric");
		} 
		
		String a = "123";
		if (is_numeric(a)) {
			System.out.println(a+" is numeric");
		} else {
			System.out.println(a+" not numeric");
		}
		
		String b = "12ad";
		if (is_numeric(b)) {
			System.out.println(b+" is numeric");
		} else {
			System.out.println(b+" not numeric");
		} 
 	}

	/**
	 * check a string whether is numeric or not 
	 * @param String str 
	 * @return boolean true or false
	 */
	public static boolean is_numeric(String str) {
		try {
			Double d= Double.valueOf(str);
		} catch (java.lang.Exception e) {
			return false;
		}
		return true;
	}
}

测试输出：

123.123 is numeric
123 is numeric
12ad not numeric