Java TreeSet pollLast()方法及示例

Java.util.concurrent.TreeSet 的 pollLast() 方法是Java中的一个内置函数，它返回检索和删除最后（最高）的元素，如果这个集合是空的，则返回null。

语法

public E pollLast()

返回值： 该函数返回检索并删除最后（最高）的元素，如果这个集合是空的，则返回null。

下面的程序说明了TreeSet.pollLast()方法。

程序1 :

// Java program to demonstrate pollLast()
// method of TreeSet
  
import java.util.*;
  
class TreeSetpollLastExample1 {
    public static void main(String[] args)
    {
        // Creating a set object
        TreeSet<Integer> set
            = new TreeSet<Integer>();
  
        // Adding elements to this set
        for (int i = 10; i <= 50; i += 10)
            set.add(i);
  
        // Printing the content of the set
        System.out.println("Contents of the set: " + set);
  
        // Retrieving and removing Last element of the set
        System.out.println("The Last element of the set: "
                           + set.pollLast());
  
        // Printing the content of the set after pollLast()
        System.out.println("Contents of the set after pollLast: "
                           + set);
    }
}

输出：

Contents of the set: [10, 20, 30, 40, 50]
The Last element of the set: 50
Contents of the set after pollLast: [10, 20, 30, 40]

程序2

// Java program to demonstrate pollLast()
// method of TreeSet
  
import java.util.*;
  
class TreeSetpollLastExample2 {
    public static void main(String[] args)
    {
        // Creating a set object
        TreeSet<Integer> set
            = new TreeSet<Integer>();
  
        // Printing the content of the set
        System.out.println("Contents of the set: "
                           + set);
  
        // Retrieving and removing Last element of the set
        System.out.println("The Last element of the set: "
                           + set.pollLast());
    }
}

输出：

Contents of the set: []
The Last element of the set: null