Java API提供的集合框架中Set接口下的集合对象默认是不能存储重复对象的，这里的重复判定是按照对象实例句柄的地址来判定的，地址相同则判定为重复，地址不同不管内容如何都判定为不重复，这有时与需求不符，可以通过重写hashCode和equals方法实现按照集合元素的任意内容判定重复。

public class Employee implements Cloneable

{

	private int id;

	private String name;

	public Employee(int id, String name)

	{

		super();

		this.id = id;

		this.name = name;

	}

	public int getId()

	{

		return id;

	}

	public void setId(int id)

	{

		this.id = id;

	}

	public String getName()

	{

		return name;

	}

	public void setName(String name)

	{

		this.name = name;

	}

	@Override

	public int hashCode()

	{

		return this.getId();

	}

	@Override

	public boolean equals(Object obj)

	{

		if (this == obj)

			return true;

		if (obj == null)

			return false;

		if (getClass() != obj.getClass())

			return false;

		Employee other = (Employee) obj;

		if (id != other.id)

			return false;

		return true;

	}

	@Override

	protected Employee clone() throws CloneNotSupportedException

	{

		return (Employee) super.clone();

	}

}

public class Test

{

	public static void main(String[] args) throws CloneNotSupportedException

	{

		Set<Employee> set = createEmployeeSet();

		System.err.println(set.size());

		for (Employee e : set)

		{

			System.out.println(e.getId() + "  " + e.getName());

		}

	}

	public static Set<Employee> createEmployeeSet()

			throws CloneNotSupportedException

	{

		Set<Employee> set = new HashSet<Employee>();

		Employee e1 = new Employee(1, "xmc1");

		Employee e2 = new Employee(2, "xmc2");

		Employee e3 = e1.clone();

		Employee e4 = new Employee(2, "xmc3");

		set.add(e1);

		set.add(e2);

		set.add(e3);

		set.add(e4);

		return set;

	}

}