Java中的 ConcurrentSkipListSet floor() 方法

Java .util.concurrent.ConcurrentSkipListSet的floor()方法是Java中的一个内置函数，它返回这个集合中小于或等于给定元素的最大元素，如果没有这样的元素，则返回 null。

句法：

ConcurrentSkipListSet.floor(E e)

参数：该函数接受单个参数e ，即要匹配的值。

返回值：该函数返回小于或等于e的最大元素，如果没有这样的元素，则返回 null。

异常：该函数抛出以下异常：

ClassCastException – 如果指定的元素无法与集合中当前的元素进行比较。

NullPointerException – 如果指定元素为 null

下面的程序说明了 ConcurrentSkipListSet.floor() 方法：

方案一：

// Java program to demonstrate floor()
// method of ConcurrentSkipListSet
  
import java.util.concurrent.*;
  
class ConcurrentSkipListSetFloorExample1 {
    public static void main(String[] args)
    {
        // Creating a set object
        ConcurrentSkipListSet
            Lset = new ConcurrentSkipListSet();
  
        // Adding elements to this set
        for (int i = 10; i <= 50; i += 10)
            Lset.add(i);
  
        // Finding floor of 20 in the set
        System.out.println("The floor of 20 in the set "
                           + Lset.floor(20));
  
        // Finding floor of 39 in the set
        System.out.println("The floor of 39 in the set "
                           + Lset.floor(39));
  
        // Finding floor of 9 in the set
        System.out.println("The floor of 10 in the set "
                           + Lset.floor(9));
    }
}

输出：

The floor of 20 in the set 20
The floor of 39 in the set 30
The floor of 10 in the set null

程序 2：在 floor() 中显示 NullPointerException 的程序。

// Java program to demonstrate floor()
// method of ConcurrentSkipListSet
  
import java.util.concurrent.*;
  
class ConcurrentSkipListSetFloorExample2 {
    public static void main(String[] args)
    {
        // Creating a set object
        ConcurrentSkipListSet
            Lset = new ConcurrentSkipListSet();
  
        // Adding elements to this set
        for (int i = 10; i <= 50; i += 10)
            Lset.add(i);
  
        // Trying to find the floor of null
        try {
            System.out.println("The floor of null in the set "
                               + Lset.floor(null));
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

输出：

Exception: java.lang.NullPointerException

参考： https: Java/util/concurrent/ConcurrentSkipListSet.html#floor-E-