Java WeakHashMap put()用法及代碼示例

WeakHashMap的java.util.WeakHashMap.put()方法用於將映射插入Map。這意味著我們可以將特定的鍵及其映射的值插入到特定的映射中。如果傳遞了現有鍵，則以前的值將被新值替換。如果傳遞了新的配對，則該配對將整體插入。

用法:

Weak_Hash_Map.put(key, value)

參數：該方法有兩個參數，均為WeakHashMap的Object類型。

key:這是指需要插入Map中進行映射的關鍵元素。
value:這是指以上鍵將映射到的值。

返回值：如果傳遞了現有鍵，則返回先前的值。如果傳遞了新對，則返回NULL。

以下程序用於說明java.util.WeakHashMap.put()方法的用法：
示例1:傳遞現有 key 時。

// Java code to illustrate the put() method 
import java.util.*; 
  
public class Weak_Hash_Map_Demo { 
    public static void main(String[] args) 
    { 
  
        // Creating an empty WeakHashMap 
        Map<Integer, String> weak_hash = new 
                  WeakHashMap<Integer, String>(); 
  
        // Mapping string values to int keys 
        weak_hash.put(10, "Geeks"); 
        weak_hash.put(15, "4"); 
        weak_hash.put(20, "Geeks"); 
        weak_hash.put(25, "Welcomes"); 
        weak_hash.put(30, "You"); 
  
        // Displaying the WeakHashMap 
        System.out.println("Initial Mappings are: " +  
                                           weak_hash); 
  
        // Inserting existing key along with new value 
        String returned_value =  
                     (String)weak_hash.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: " + weak_hash); 
    } 
}

輸出：

Initial Mappings are: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks}
Returned value is: Geeks
New map is: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=All}

示例2:傳遞新 key 時。

// Java code to illustrate the put() method 
import java.util.*; 
  
public class Weak_Hash_Map_Demo { 
    public static void main(String[] args) 
    { 
  
        // Creating an empty WeakHashMap 
        Map<Integer, String> weak_hash = new 
                 WeakHashMap<Integer, String>(); 
  
        // Mapping string values to int keys 
        weak_hash.put(10, "Geeks"); 
        weak_hash.put(15, "4"); 
        weak_hash.put(20, "Geeks"); 
        weak_hash.put(25, "Welcomes"); 
        weak_hash.put(30, "You"); 
  
        // Displaying the WeakHashMap 
        System.out.println("Initial Mappings are: " +  
                                          weak_hash); 
  
        // Inserting existing key along with new value 
        String returned_value =  
                      (String)weak_hash.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: " + weak_hash); 
    } 
}

輸出：

Initial Mappings are: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks}
Returned value is: null
New map is: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks, 50=All}

注意：可以對具有不同數據類型的變化和組合的任何類型的映射執行相同的操作。

相關用法

注：本文由純淨天空篩選整理自Chinmoy Lenka大神的英文原創作品 WeakHashMap put() Method in Java。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。