@Override
  public void add(E e) {
    if (!list.contains(e)) {
      list.addFirst(e);
    }
  }

/**
 * 集合的接口
 */
public interface Set<E> {
  void add(E e);//添加 <——<不能添加重复元素
  void remove(E e);//移除
  int getSize();//获取大小
  boolean isEmpty();//是否为空
  boolean contains(E e);//是否包含元素
  
}

public class LinkedListSet<E> implements Set<E> {

  private LinkedList<E> list;


  public LinkedListSet() {
    list = new LinkedList<E>();
  }


  @Override
  public int getSize() {
    return list.getSize();
  }

  @Override
  public boolean isEmpty() {
    return list.isEmpty();
  }

  @Override
  public boolean contains(E e) {
    return list.contains(e);
  }

  @Override
  public void add(E e) {
    if (!list.contains(e)) {
      list.addFirst(e);
    }
  }


  @Override
  public void remove(E e) {
    list.removeElement(e);
  }
}

import java.util.ArrayList;

public class LinkedListSetTestDemo {
  public static void main(String[] args) {

    System.out.println("Pride and Prejudice");
    //新建一个ArrayList存放单词
    ArrayList<String> words1 = new ArrayList<>();
    //通过这个方法将书中所以单词存入word1中
    FileOperation.readFile("pride-and-prejudice.txt", words1);
    System.out.println("Total words : " + words1.size());

    LinkedListSet<String> set1 = new LinkedListSet<>();
    //增强for循环，定一个字符串word去遍历words
    //底层的话会把ArrayList words1中的值一个一个的赋值给word
    for (String word : words1)
      set1.add(word);//不添加重复元素
    System.out.println("Total different words : " + set1.getSize());


    System.out.println("-------------------");
    System.out.println("Pride and Prejudice");
    //新建一个ArrayList存放单词
    ArrayList<String> words2 = new ArrayList<>();
    //通过这个方法将书中所以单词存入word1中
    FileOperation.readFile("a-tale-of-two-cities.txt", words2);
    System.out.println("Total words : " + words2.size());

    LinkedListSet<String> set2 = new LinkedListSet<>();
    //增强for循环，定一个字符串word去遍历words
    //底层的话会把ArrayList words1中的值一个一个的赋值给word
    for (String word : words2)
      set2.add(word);//不添加重复元素
    System.out.println("Total different words : " + set2.getSize());

  }
}