根據需求用字符串正則的點也試著寫了下

	public?static?void?main(String[]?args)?{
		//?TODO?Auto-generated?method?stub
		Scanner?scan?=?new?Scanner(System.in);
		System.out.println("請輸入數字");
		String?in?=?scan.next();
		while(true){
			if(in.matches("\\d+")){
				System.out.println("輸入為："+in);
				break;
			}else{
				System.out.println("輸入錯誤，請重新輸入");
				in?=?scan.next();
			}
		}

	}

不習慣你的代碼風格，根據你的需求我單獨寫個示例吧

public?static?void?main(String[]?args)?{
????????boolean?input_right?=?false;
????????int?input?=?0;
????????do?{
????????????Scanner?console?=?new?Scanner(System.in);
????????????System.out.print("請輸入數字：");
????????????try?{
????????????????input?=?console.nextInt();
????????????????input_right?=?true;
????????????}?catch?(Exception?e)?{
????????????????System.out.println("輸入錯誤！");
????????????}
????????}?while(!input_right);
????????System.out.println("用戶輸入："?+?input);
????}