一个 TreeSet 的例子

原文地址：http://www.programcreek.com/2009/02/a-simple-treeset-example/

以下是一个非常简单的 TreeSet 示例，从这个例子中你可以知道：

• TreeSet 为何是排序的
• 如何迭代 TreeSet
• 如何查空
• 如何检索第一个/最后一个元素
• 如何删除元素

如果您想了解有关 Java Collection 的更多信息，可以查看 Java Collection 层次结构图。

import java.util.Iterator;
import java.util.TreeSet;

public class TreeSetExample {

   public static void main(String[] args) {
    System.out.println("Tree Set Example!\n");
    TreeSet<Integer> tree = new TreeSet<Integer>();
    tree.add(12);
    tree.add(63);
    tree.add(34);
    tree.add(45);

    // here it test it's sorted, 63 is the last element. see output below
    Iterator<Integer> iterator = tree.iterator();
    System.out.print("Tree set data: ");

    // Displaying the Tree set data
    while (iterator.hasNext()) {
        System.out.print(iterator.next() + " ");
    }
    System.out.println();

    // Check empty or not
    if (tree.isEmpty()) {
        System.out.print("Tree Set is empty.");
    } else {
        System.out.println("Tree Set size: " + tree.size());
    }

    // Retrieve first data from tree set
    System.out.println("First data: " + tree.first());

    // Retrieve last data from tree set
    System.out.println("Last data: " + tree.last());

    if (tree.remove(45)) { // remove element by value
        System.out.println("Data is removed from tree set");
    } else {
        System.out.println("Data doesn't exist!");
    }
    System.out.print("Now the tree set contain: ");
    iterator = tree.iterator();

    // Displaying the Tree set data
    while (iterator.hasNext()) {
        System.out.print(iterator.next() + " ");
    }
    System.out.println();
    System.out.println("Now the size of tree set: " + tree.size());

    // Remove all
    tree.clear();
    if (tree.isEmpty()) {
        System.out.print("Tree Set is empty.");
    } else {
        System.out.println("Tree Set size: " + tree.size());
    }
   }
}

输出结果为：

Tree Set Example!

Tree set data: 12 34 45 63
Tree Set size: 4

First data: 12
Last data: 63

Data is removed from tree set

Now the tree set contain: 12 34 63
Now the size of tree set: 3

Tree Set is empty.