TreeMap的java.util.TreeMap.put()方法用于将映射插入Map。这意味着我们可以将特定的键及其映射到的值插入到特定的映射中。如果传递了现有键，则以前的值将被新值替换。如果传递了新的配对，则该配对将整体插入。

用法:

Tree_Map.put(key, value)

参数：该方法有两个参数，它们都是TreeMap的Object类型。

key:这是指需要插入Map中进行映射的关键元素。

value:这是指以上键将映射到的值。

返回值：如果传递了现有键，则返回先前的值。如果传递了新对，则返回NULL。

以下程序用于说明java.util.TreeMap.put()方法的用法：

示例1:传递现有 key 时。

// Java code to illustrate the put() method

import java.util.*;

public class Tree_Map_Demo {

public static void main(String[] args)

{

// Creating an empty TreeMap

TreeMap tree_map = new TreeMap();

// Mapping string values to int keys

tree_map.put(10, "Geeks");

tree_map.put(15, "4");

tree_map.put(20, "Geeks");

tree_map.put(25, "Welcomes");

tree_map.put(30, "You");

// Displaying the TreeMap

System.out.println("Initial Mappings are: " + tree_map);

// Inserting existing key along with new value

String returned_value = (String)tree_map.put(20, "All");

// Verifying the returned value

System.out.println("Returned value is: " + returned_value);

// Displayin the new map

System.out.println("New map is: " + tree_map);

}

}

输出：

Initial Mappings are: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You}

Returned value is: Geeks

New map is: {10=Geeks, 15=4, 20=All, 25=Welcomes, 30=You}

示例2:传递新 key 时。

// Java code to illustrate the put() method

import java.util.*;

public class Tree_Map_Demo {

public static void main(String[] args)

{

// Creating an empty TreeMap

TreeMap tree_map = new TreeMap();

// Mapping string values to int keys

tree_map.put(10, "Geeks");

tree_map.put(15, "4");

tree_map.put(20, "Geeks");

tree_map.put(25, "Welcomes");

tree_map.put(30, "You");

// Displaying the TreeMap

System.out.println("Initial Mappings are: " + tree_map);

// Inserting existing key along with new value

String returned_value = (String)tree_map.put(50, "All");

// Verifying the returned value

System.out.println("Returned value is: " + returned_value);

// Displayin the new map

System.out.println("New map is: " + tree_map);

}

}

输出：

Initial Mappings are: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You}

Returned value is: null

New map is: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You, 50=All}

注意：可以对具有不同数据类型的变化和组合的任何类型的映射执行相同的操作。