Java 中的 ConcurrentSkipListSet headSet()方法

原文:https://www . geeksforgeeks . org/concurrentskiplistset-头戴式耳机-java 中的方法/

耳机(和托儿)

java . util . concurrentskiplistset . headset()方法是 Java 中的内置函数，它返回该集合中元素严格小于 toElement 的部分的视图。返回的集合由该集合支持，因此返回集合中的更改反映在该集合中，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。

语法:

public NavigableSet headSet(E toElement)

参数:该函数接受单个参数到元素，即返回集合的高端点。

返回值:该函数返回一个导航集，它是该集合中元素严格小于 to 元素的部分的视图。

以下程序说明了 concurrentskiplistset . headset(E to element)方法: 程序 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);
    }
}

Output:

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

程序 2: 显示空指针异常的程序。

// 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);
    }
}

Output:

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

头戴式耳机(E toElement，含布尔型)

java . util . concurrentskiplistset . headset()方法是 Java 中的内置函数，它返回该集合中元素小于(或等于，如果包含为真)toElement 的部分的视图。返回的集合由该集合支持，因此返回集合中的更改反映在该集合中，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。

语法:

public NavigableSet headSet(E toElement,
                      boolean inclusive)

参数:函数接受以下参数

  • 至元素，即返回集合的高端点。 inclusive* – true if the high endpoint is to be included in the returned view.

    返回值:该函数返回一个导航集，该导航集是该集合中元素小于(或等于，如果包含为真)元素的部分的视图。

    下面的程序说明了 concurrentskiplistset . headset(E to element，布尔包含)方法:

    程序 3:

    ```java // 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             set = new ConcurrentSkipListSet();

    // 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 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);     } } ```

    Output:

    ```java 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/concurrentskiplistset . html # headSet-E-

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