第一题这样应该就可以：

public static void main(String[] args) {
    String s1 = "abcderf0";  String s2 = "adf";  boolean[]array = new boolean[128];  for(int i =0;i;i++){
        array[s2.charAt(i)] = true;  }
    StringBuilder newS1 = new StringBuilder();  for(int i=0;i;i++){ if(array[s1.charAt(i)]){ continue;  }
        newS1.append(s1.charAt(i));  }
    String res = new String(newS1);  System.out.println(res); }