Set 的其他实现类：TreeSet

public class TestTreeSet {
	public static void main(String[] args) {
		TreeSet t = new TreeSet();
		t.add(new Person(12, "b"));
		t.add(new Person(12, "d"));
		t.add(new Person(11, "c"));
		t.add(new Person(10, "b"));
		System.out.println(t);// [Person [id=10, name=b],
								// Person [id=11, name=c],
								// Person [id=12, name=b],
								// Person [id=12, name=d]]
	}
}
class Person implements Comparable {
	private Integer id;
	private String name;
	public Person(int id, String name) {
		super();
		this.id = id;
		this.name = name;
	}
	public Person() {
		super();
	}
	public Integer 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() {
		final int prime = 31;
		int result = 1;
		result = prime * result + id;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		return result;
	}
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Person other = (Person) obj;
		if (id != other.id)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}
	@Override
	public String toString() {
		return "Person [id=" + id + ", name=" + name + "]";
	}
	@Override
	public int compareTo(Object o) {
		if (o instanceof Person) {
			Person p = (Person) o;
			int i = this.getId().compareTo(p.getId());
			if (i == 0) {
				return this.getName().compareTo(p.getName());
			}
			return i;
		}
		return 0;
	}
}

public class TestTreeSet {
	public static void main(String[] args) {
		TreeSet t = new TreeSet(new Comparator() {
			@Override
			public int compare(Object o1, Object o2) {
				if (o1 instanceof Person && o2 instanceof Person) {
					Person p1 = (Person) o1;
					Person p2 = (Person) o2;
					int i = p1.getId().compareTo(p2.getId());
					if (i == 0) {
						return p1.getName().compareTo(p2.getName());
					}
					return i;
				}
				return 0;
			}
		});
		t.add(new Person(12, "b"));
		t.add(new Person(12, "a"));
		t.add(new Person(11, "c"));
		t.add(new Person(10, "b"));
		System.out.println(t);// [Person [id=10, name=b],
								// Person [id=11, name=c],
								// Person [id=12, name=a],
								// Person [id=12, name=b]]
	}
}
class Person {
	private Integer id;
	private String name;
	public Person(int id, String name) {
		super();
		this.id = id;
		this.name = name;
	}
	public Person() {
		super();
	}
	public Integer 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() {
		final int prime = 31;
		int result = 1;
		result = prime * result + id;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		return result;
	}
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Person other = (Person) obj;
		if (id != other.id)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}
	@Override
	public String toString() {
		return "Person [id=" + id + ", name=" + name + "]";
	}
}