Java ConcurrentSkipListSet headSet()用法及代码示例

headSet(E toElement)

java.util.concurrent.ConcurrentSkipListSet.headSet()方法是Java中的内置函数，它返回此集合部分的视图，这些元素的元素严格小于toElement。返回的集合受此集合支持，因此返回的集合中的更改将反映在此集合中，反之亦然。返回的集合支持该集合支持的所有可选集合操作。

用法:

public NavigableSet headSet(E toElement)

参数：该函数接受元素的单个参数，即返回集的高端点。

返回值：该函数返回一个NavigableSet，该视图是此集合中元素严格小于toElement的部分的视图。

以下示例程序旨在说明ConcurrentSkipListSet.headSet(E toElement)方法：
示例1:

// Java Program Demonstrate headSet() 
// method of ConcurrentSkipListSet */ 
import java.util.NavigableSet; 
import java.util.concurrent.ConcurrentSkipListSet; 
  
class ConcurrentSkipListSetHeadSetExample1 { 
    public static void main(String[] args) 
    { 
  
        // Initializing the set 
        ConcurrentSkipListSet<Integer> 
            set = new ConcurrentSkipListSet<Integer>(); 
  
        // Adding elements to this set 
        for (int i = 10; i <= 50; i += 10) 
            set.add(i); 
  
        // Creating a headSet object with upper limit 30 
        NavigableSet<Integer> hd_set = set.headSet(30); 
  
        // Printing the elements of the set 
        System.out.println("Contents of the set: " + set); 
  
        // Printing the elements of the headSet set 
        System.out.println("Contents of the headset"
                           + " with upper limit 30: "
                           + hd_set); 
    } 
}

输出：

Contents of the set: [10, 20, 30, 40, 50]
Contents of the headset with upper limit 30: [10, 20]

示例2:显示NullPointerException的程序。

// Java Program Demonstrate headSet() 
// method of ConcurrentSkipListSet */ 
import java.util.NavigableSet; 
import java.util.concurrent.ConcurrentSkipListSet; 
  
class ConcurrentSkipListSetHeadSetExample2 { 
    public static void main(String[] args) 
    { 
  
        // Initializing the set 
        ConcurrentSkipListSet<Integer> 
            set = new ConcurrentSkipListSet<Integer>(); 
  
        // Adding elements to this set 
        for (int i = 10; i <= 50; i += 10) 
            set.add(i); 
  
        // Printing the elements of the set 
        System.out.println("Contents of the set: " + set); 
  
        try { 
            // Trying to creating a headSet object with upper limit null 
            NavigableSet<Integer> hd_set = set.headSet(null); 
        } 
  
        catch (Exception e) { 
            System.out.println("Exception: " + e); 
        } 
        // Printing the elements of the headSet set 
        // System.out.println("Contents of the headset" 
+" with upper limit 30: "+ hd_set); 
    } 
}

输出：

Contents of the set: [10, 20, 30, 40, 50]
Exception: java.lang.NullPointerException

headSet(E toElement, boolean inclusive)

java.util.concurrent.ConcurrentSkipListSet.headSet()方法是Java中的内置函数，该函数返回该集合中元素小于(或等于，如果包含，则为true)toElement的部分的视图。返回的集合受此集合支持，因此返回的集合中的更改将反映在此集合中，反之亦然。返回的集合支持该集合支持的所有可选集合操作。

用法:

public NavigableSet headSet(E toElement,
                      boolean inclusive)

参数：该函数接受以下参数

toElement即返回集的高端点。
inclusive–如果高端端点将包含在返回的视图中，则为true。

返回值：该函数返回一个NavigableSet，该视图是此集合中元素小于(或等于，如果包含在内，则为true)toElement的部分的视图。

以下示例程序旨在说明ConcurrentSkipListSet.headSet(E toElement，包含布尔值)方法：

示例3:

// Java Program Demonstrate headSet() 
// method of ConcurrentSkipListSet */ 
  
import java.util.NavigableSet; 
import java.util.concurrent.ConcurrentSkipListSet; 
  
class ConcurrentSkipListSetHeadSetExample3 { 
    public static void main(String[] args) 
    { 
  
        // Initializing the set 
        ConcurrentSkipListSet<Integer> 
            set = new ConcurrentSkipListSet<Integer>(); 
  
        // Adding elements to this set 
        for (int i = 10; i <= 50; i += 10) 
            set.add(i); 
  
        // Creating a headSet object with upper limit 30 inclusive 
        NavigableSet<Integer> hd_set = set.headSet(30, true); 
  
        // Printing the elements of the set 
        System.out.println("Contents of the set: " + set); 
  
        // Printing the elements of the headSet set 
        System.out.println("Contents of the headset"
                           + " with upper limit 30 inclusive: "
                           + hd_set); 
    } 
}

输出：

Contents of the set: [10, 20, 30, 40, 50]
Contents of the headset with upper limit 30 inclusive: [10, 20, 30]

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

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注：本文由纯净天空筛选整理自rupesh_rao大神的英文原创作品 ConcurrentSkipListSet headSet() method in Java。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。