去除arraylist容器中的相同的对象元素的方法

<span class="keyword" style="background-color: rgb(250, 250, 250); font-size: 1em; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', Consolas, 'Courier New', monospace;">boolean</span><span style="color: black; background-color: rgb(250, 250, 250); font-size: 1em; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', Consolas, 'Courier New', monospace;"> retainAll(Collection<?> c); </span>

<pre name="code" class="html">List<Employee> <span style="font-family: Arial, Helvetica, sans-serif;">employeeOfIntermediarys </span><span style="font-family: Arial, Helvetica, sans-serif;">= new ArrayList<Employee>();
</span><pre name="code" class="html">List<Employee> <span style="font-family: Arial, Helvetica, sans-serif;">tempList </span><span style="font-family: Arial, Helvetica, sans-serif;">= new ArrayList<Employee>();</span>

if(tempList != null){
<span style="white-space:pre">	</span>//去掉<span style="font-family: Arial, Helvetica, sans-serif;">tempList 中与</span><span style="font-family: Arial, Helvetica, sans-serif;">employeeOfIntermediarys 中</span>相同的元素，在合并
	List<Employee> eoiList = new ArrayList<Employee>(employeeOfIntermediarys);
	if (eoiList.retainAll(tempList)) {
		tempList.removeAll(eoiList);
	}

	employeeOfIntermediarys.addAll(tempList);
}

public class Book {

	private int id;
	private String nameString;
	private String writer;
	
	public Book(){
		id= -1;
		nameString = "";
		writer = "";
	}

List<Book> books = new ArrayList<Book>();
  List<Book> tempList = new ArrayList<Book>();
  
  Book book1 = new Book();
  book1.setId(1);
  book1.setNameString("dkjdf");
  
  Book book2 = new Book();
  book2.setId(2);
  book2.setNameString("到加福禄寿");
  
  Book book3 = new Book();
  book3.setId(3);
  book3.setNameString("dj地方");
  
  Book book4 = new Book();
  book4.setId(4);
  book4.setNameString("dkjdf");
  
  Book book5 = new Book();
  book5.setId(5);
  book5.setNameString("到加福禄寿");
  
  Book book6 = new Book();
  book6.setId(6);
  book6.setNameString("dj地方");
  
  
  books.add(book1);
  books.add(book2);
  books.add(book5);
  books.add(null);
  
  tempList.add(book1);
  tempList.add(book4);
  tempList.add(null);
  tempList.retainAll(books);
  System.out.println(tempList.get(0).booktoString());

	@Override
	public boolean equals(Object c){
		if (!(c instanceof Employee)) {
			return false;
		}
		Employee eoi = (Employee) c;
		if (eoi.getUserGuid().equals(userGuid)) {
			return true;
		}
		return false;		
	}