Java 中的 TreeMap ceilingKey()带示例

原文:https://www . geesforgeks . org/tree map-ceiling key-in-Java-with-examples/

树状图类的 ceilingKey()函数返回大于或等于给定键的最小键，如果该键不存在，则返回 null。

语法:

public K ceilingKey(K key)

参数:该方法接受一个强制参数键，这是需要搜索的键。

返回值:该方法返回大于等于给定键值的最小键。 如果没有这样的键，则返回 null。

异常:该方法抛出以下异常:

  • class castexception–如果指定的键无法与给定的键值进行比较，则抛出。
  • NullPointRexception–如果给定键为空，并且映射使用自然排序，或者比较器不允许空值，则抛出。

以下是说明 ceilingKey()方法的示例:

程序 1: 演示使用 ceilingKey()方法创建带有比较器的树形图

import java.util.*;

public class Main {
    public static void main(String[] args)
    {

        // creating tree map
        NavigableMap<Integer, String>
            treemap = new TreeMap<Integer,
                                  String>((a, b)
                                              -> ((a > b)
                                                      ? 1
                                                      : ((a == b)
                                                             ? 0
                                                             : -1)));

        // populating tree map
        treemap.put(1, " A ");
        treemap.put(2, " B ");
        treemap.put(3, " C ");
        treemap.put(4, " D ");
        treemap.put(6, " E ");
        try {
            System.out.println("Ceiling key entry for 5: "
                               + treemap.ceilingKey(5));
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

Output:

Ceiling key entry for 5: 6

程序 2: 演示在没有任何比较器的情况下，对树图使用 ceilingKey()方法

import java.util.*;

public class Main {
    public static void main(String[] args)
    {

        // creating tree map
        NavigableMap<Integer, String>
            treemap = new TreeMap<Integer, String>();

        // populating tree map
        treemap.put(1, " A ");
        treemap.put(2, " B ");
        treemap.put(3, " C ");
        treemap.put(4, " D ");
        treemap.put(6, " E ");
        treemap.put(7, " F ");

        // Since 6 is the least value greater than 5,
        // it is returned as the key.
        System.out.println("Ceiling key entry for 5: "
                           + treemap.ceilingKey(5));
    }
}

Output:

Ceiling key entry for 5: 6

程序 3: 演示当 ceilingKey()方法将返回 null 时的用法

import java.util.*;

public class Main {
    public static void main(String[] args)
    {

        // creating tree map
        NavigableMap<Integer, String>
            treemap = new TreeMap<Integer, String>();

        // populating tree map
        treemap.put(1, " A ");
        treemap.put(2, " B ");
        treemap.put(3, " C ");
        treemap.put(4, " E ");
        treemap.put(5, " D ");

        // Since 10 is not present in the Map
        // and neither any Key is present greater than 10
        // Hence this will return null
        System.out.println("Ceiling key entry for 10: "
                           + treemap.ceilingKey(10));
    }
}

Output:

Ceiling key entry for 10: null

程序 4: 显示空指针异常

import java.util.*;

public class Main {
    public static void main(String[] args)
    {

        // creating tree map
        TreeMap<Integer, String>
            treemap = new TreeMap<Integer, String>();

        // populating tree map
        treemap.put(2, " two ");
        treemap.put(1, " one ");
        treemap.put(3, " three ");
        treemap.put(6, " six ");
        treemap.put(5, " five ");

        try {
            // returns a NullPointerException
            // as key value can't be null
            // because of natural ordering
            System.out.println("Ceiling key entry for null value : "
                               + treemap.ceilingKey(null));
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

Output:

Exception: java.lang.NullPointerException

程序 5: 演示 ClassCastException

import java.util.*;

public class Main {
    public static void main(String[] args)
    {

        // creating tree map
        NavigableMap<Object, String>
            treemap = new TreeMap<Object, String>();

        // populating tree map
        treemap.put(1, " A ");
        treemap.put(2, " B ");
        treemap.put(3, " C ");
        treemap.put(4, " E ");
        treemap.put(5, " D ");

        try {
            // returns ClassCastException
            // as we cannot compare a String object with an Integer object
            System.out.println("Ceiling key entry for \"asd\": "
                               + treemap.ceilingKey(new String("asd")));
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

Output:

Exception: java.lang.ClassCastException: 
           java.lang.Integer cannot be cast to java.lang.String

版权属于：月萌API www.moonapi.com，转载请注明出处

本文链接：https://moonapi.com/news/25912.html