Java 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。

语法

ConcurrentSkipListSet.floor(E e)

参数： 该函数接受一个参数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，则返回空。

异常： 该函数会抛出以下异常。

• ClassCastException - 如果指定的元素不能与当前集合中的元素进行比较。
• NullPointerException - 如果指定的元素是空的。

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

程序1 :

// 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<Integer>
            Lset = new ConcurrentSkipListSet<Integer>();
  
        // 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： 显示floor()中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<Integer>
            Lset = new ConcurrentSkipListSet<Integer>();
  
        // 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

参考资料: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentSkipListSet.html#floor-E-