Java 中的 TreeMap lowerEntry()方法，带示例

原文:https://www . geesforgeks . org/tree map-lowerentry-method-in-Java-with-examples/

Java . util . treemap类的lowerrentry()方法用于返回与严格小于给定键的最大键相关联的键值映射，如果没有这样的键 语法:

public Map.Entry lowerEntry(K key)

参数:该方法以键为参数，寻找下条目。 返回值:该方法返回一个最大键小于键的条目，如果没有这样的键则为空。 异常:如果指定的键为空，并且该映射使用自然排序，或者其比较器不允许空键，则该方法抛出 NullPointerException 。 以下是举例说明lowerrentry()方法 T20】例 1:T22】

Java 语言(一种计算机语言，尤用于创建网站)

// Java program to demonstrate
// lowerEntry() method
// for <Integer, String>

import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        try {

            // creating object of TreeMap<Integer, String>
            TreeMap<Integer, String>
                treemap = new TreeMap<Integer, String>();

            // populating tree map
            treemap.put(1, "One");
            treemap.put(2, "Two");
            treemap.put(3, "Three");
            treemap.put(4, "Four");
            treemap.put(5, "Five");

            // printing the TreeMap
            System.out.println("TreeMap: " + treemap);

            // getting lowerEntry value for 3
            // using lowerEntry() method
            Map.Entry<Integer, String>
                value
                = treemap.lowerEntry(3);

            // printing the value
            System.out.println("The lowerEntry value "
                               + " for 3: " + value);
        }

        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output: 

TreeMap: {1=One, 2=Two, 3=Three, 4=Four, 5=Five}
The lowerEntry value  for 3: 2=Two

例 2: 为零点异常T4】

Java 语言(一种计算机语言，尤用于创建网站)

// Java program to demonstrate
// lowerEntry() method
// for NullPointerException

import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        try {

            // creating object of TreeMap<Integer, String>
            TreeMap<Integer, String>
                treemap = new TreeMap<Integer, String>();

            // populating tree map
            treemap.put(1, "One");
            treemap.put(2, "Two");
            treemap.put(3, "Three");
            treemap.put(4, "Four");
            treemap.put(5, "Five");

            // printing the TreeMap
            System.out.println("TreeMap: " + treemap);

            // getting lowerEntry value for null
            // using lowerEntry() method
            System.out.println("Trying to get"
                               + " the lowerEntry value"
                               + " for value NULL");

            Map.Entry<Integer, String>
                value
                = treemap.lowerEntry(null);

            // printing the value
            System.out.println("Value is: " + value);
        }

        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output: 

TreeMap: {1=One, 2=Two, 3=Three, 4=Four, 5=Five}
Trying to get the lowerEntry value for value NULL
Exception thrown : java.lang.NullPointerException

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