Java 中的 SortedSet headSet()方法

原文:https://www . geesforgeks . org/sorted set-headset-method-in-Java/

Java 中 SortedSet 接口的 headSet()方法用于返回该集合中元素严格小于参数 toElement 的部分的视图。

* The collection returned by this method is supported by this collection, so the changes in the returned collection are reflected in this collection, and vice versa.* The collection returned by this method supports all optional collection operations supported by this collection.

注意:如果试图插入一个超出其范围的元素，这个方法返回的集合将抛出 IllegalArgumentException 。

语法 :

SortedSet headSet(E toElement)

其中，E 是该集合维护的元素类型。

参数:该函数接受单个参数到元素，代表返回集合的高端点(不包括)。

返回值:返回集合中当前最后一个或最高的元素。

异常:

  • [T0】 ClassCastException 【T1]: If the toElement is incompatible with the comparator of this set (or if the set has no comparator and toElement does not implement compatible), a classcasteexception will be thrown.
  • null pointer exception : if the parameter toelement is null, a null pointer exception will be thrown.
  • [T0】 IllegalArgumentException 【T1]: It throws an IllegalArgumentException. This set itself has a restricted range, and the parameter toelement is outside the range boundary.

下面的程序说明了上述方法:

程序 1 :

// A Java program to demonstrate
// working of SortedSet
import java.util.SortedSet;
import java.util.TreeSet;

public class Main {
    public static void main(String[] args)
    {
        // Create a TreeSet and inserting elements
        SortedSet<Integer> s = new TreeSet<>();

        // Adding Element to SortedSet
        s.add(1);
        s.add(5);
        s.add(2);
        s.add(3);
        s.add(9);

        // Returning the set with elements
        // strictly less than the passed value
        System.out.print("Elements strictly less than 7 in set are : "
                         + s.headSet(7));
    }
}

输出:

Elements strictly less than 7 in set are : [1, 2, 3, 5]

程序二 :

// A Java program to demonstrate
// working of SortedSet
import java.util.SortedSet;
import java.util.TreeSet;

public class Main {
    public static void main(String[] args)
    {
        // Create a TreeSet and inserting elements
        SortedSet<String> s = new TreeSet<>();

        // Adding Element to SortedSet
        s.add("Geeks");
        s.add("For");
        s.add("Geeks");
        s.add("Code");
        s.add("It");

        // Returning the set with elements
        // strictly less than the passed value
        System.out.print("Element strictly less than Z in set is : "
                         + s.headSet("Z"));
    }
}

输出:

Element strictly less than Z in set is : [Code, For, Geeks, It]

参考:https://docs . Oracle . com/javase/10/docs/API/Java/util/sorted set . html # headSet(E)

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