Java TreeSet，Collections使用

1、建立TreeSet實例

public static void main(String[] args) {
		TreeSet set = new TreeSet();
		
		set.add("C");
		set.add("B");
		set.add("A");
		set.add("F");
		set.add("D");
		System.out.println(set);
	}

　　輸出

[A, B, C, D, F]

　　輸出是有序的。

 

2、TreeSet實例，按字符倒敘排列

實現了Comparator接口

public class TreeSetTest3 {
	public static void main(String[] args) {
		TreeSet<String> set = new TreeSet(new MyComparator() );
		set.add("C");
		set.add("B");
		set.add("A");
		set.add("F");
		set.add("D");
		System.out.println(set);
	
	}
}

class MyComparator implements Comparator{


	public int compare(Object o1, Object o2) {
		
		String s1 = (String) o1;
		String s2 = (String) o2;
		
		return s2.compareTo(s1);
	}
	
}

　　打印：

[F, D, C, B, A]

 

3、按數字倒敘排列

public class TreeSetTest2 {

	public static void main(String[] args) {
		TreeSet set= new TreeSet(new Comparator() {

			public int compare(Object o1, Object o2) {
				int i1 = ((Person) o1).score;
				int i2 = ((Person) o2).score;
				return i2 - i1;
			}
			
		});
		Person p1 = new Person(100);
		Person p2 = new Person(60);
		Person p3 = new Person(70);
		Person p4 = new Person(50);
		
		set.add(p1);
		set.add(p2);
		set.add(p3);
		set.add(p4);
		System.out.println(set);
	}
}

class Person{
	
	int score;
	
	public Person(int score){
		this.score = score;
	}
	

	@Override
	public String toString() {
		
		return String.valueOf(this.score);
	}
}

　　打印結果

[100, 70, 60, 50]

 

4、使用Collections降序

public class CollectionsTest {
	public static void main(String[] args) {
		LinkedList list = new LinkedList();
		list.add(new Integer(5));
		list.add(new Integer(25));
		list.add(new Integer(15));
		list.add(new Integer(35));
		list.add(new Integer(1));
		Comparator r =  Collections.reverseOrder();
		Collections.sort(list, r);
		System.out.println(list);
		
	}
}

　　[35, 25, 15, 5, 1]