java中判断是否是数字

package com.javabase.sss;

import java.util.Scanner;

public class Zhuang {

	//判断是否是数字
	public static boolean isChar(char c) {
		if (c >= '0' && c <= '9') {
			return true;
		} else {
			return false;
		}
	}

	public static void main(String[] args) {

		boolean b = false;

		Scanner input = new Scanner(System.in);
		System.out.print("请输入数字: ");
		String str = input.nextLine();
		for (int i = 0; i < str.length(); i++) {
			if (!isChar(str.charAt(i))) {
				b = false;
				break;
			}
			b = true;
		}

		if ( b == true) {
			System.out.println("是数字");
		} else {
			System.out.println("不是数字");
		}

	}

}