Java WeakHashMap keySet()用法及代碼示例

Java中的java.util.WeakHashMap.keySet()方法用於從哈希圖中包含的關鍵元素中創建一個集合。它本質上返回鍵的集合視圖，或者我們可以創建一個新集合並將鍵元素存儲在其中。

用法:

Weak_Hash_Map.keySet()

參數：該方法不帶任何參數。

返回值：該方法返回具有弱哈希映射鍵的集合。

以下程序用於說明java.util.WeakHashMap.keySet()方法的用法：
示例1:將字符串值映射到整數鍵。

// Java code to illustrate the keySet() 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); 
  
        // Using keySet() to get the set view of keys 
        System.out.println("The set is: " +  
                                  weak_hash.keySet()); 
    } 
}

輸出：

Initial Mappings are: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks}
The set is: [30, 15, 10, 25, 20]

示例2:將整數值映射到字符串鍵。

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

輸出：

Initial Mappings are: {Welcomes=25, 4=15, You=30, Geeks=20}
The set is: [Welcomes, 4, You, Geeks]

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 keySet() 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。