//假设已知随即凌乱字符
    String a = "1n21ewmnd22 asmnciushvla*/-*/!@#$%^&*  ()(*&^";
    //定义接收b;
    String b = ""; 
    for (int i = 0; i < a.length(); i++) {
    //是否含有数字,有则接收
        if ("1234567890".contains(a.charAt(i)+"")) {
            b+=a.charAt(i);
        }
    }
    //最后输出
    System.out.println(b);