Java ConcurrentHashMap get()用法及代碼示例

java.util.concurrent.ConcurrentHashMap的get()方法是Java中的內置函數，它接受鍵作為參數並返回映射到它的值。如果作為參數傳遞的鍵不存在映射，則返回null。

用法:

Concurrent.get(Object key_element)

參數：該方法接受對象類型的單個參數key_element，該參數表示應該返回其關聯值的鍵。

返回值：該方法返回與參數中的key_element關聯的值。

異常：當指定的key_element為null時，該函數將引發NullPointerException。

以下程序說明了java.util.concurrent.ConcurrentHashMap.get()方法的用法：

示例1:該程序涉及將字符串值映射到整數鍵。

// Java Program Demonstrate get() 
// method of ConcurrentHashMap 
  
import java.util.concurrent.*; 
  
class GFG { 
    public static void main(String[] args) 
    { 
  
        ConcurrentHashMap<Integer, String> 
            chm = new ConcurrentHashMap<Integer, String>(); 
  
        chm.put(100, "Geeks"); 
        chm.put(101, "for"); 
        chm.put(102, "Geeks"); 
        chm.put(103, "Contribute"); 
  
        // Displaying the HashMap 
        System.out.println("The Mappings are: "); 
        System.out.println(chm); 
  
        // Display the value of 100 
        System.out.println("The Value associated to "
                           + "100 is : " + chm.get(100)); 
  
        // Getting the value of 103 
        System.out.println("The Value associated to "
                           + "103 is : " + chm.get(103)); 
    } 
}

輸出：

The Mappings are: 
{100=Geeks, 101=for, 102=Geeks, 103=Contribute}
The Value associated to 100 is : Geeks
The Value associated to 103 is : Contribute

示例2:該程序涉及將整數值映射到字符串鍵。

// Java Program Demonstrate get() 
// method of ConcurrentHashMap 
  
import java.util.concurrent.*; 
  
class GFG { 
    public static void main(String[] args) 
    { 
  
        ConcurrentHashMap<String, Integer> 
            chm = new ConcurrentHashMap<String, Integer>(); 
  
        chm.put("Geeks", 100); 
        chm.put("GFG", 10); 
        chm.put("GeeksforGeeks", 25); 
        chm.put("Contribute", 102); 
  
        // Displaying the HashMap 
        System.out.println("The Mappings are: "); 
        System.out.println(chm); 
  
        // Display the value of Geeks 
        System.out.println("The Value associated to "
                           + "Geeks is : " + chm.get("Geeks")); 
  
        // Getting the value of Contribute 
        System.out.println("The Value associated to "
                           + "Contribute is : " + chm.get("Contribute")); 
    } 
}

輸出：

The Mappings are: 
{GeeksforGeeks=25, Geeks=100, GFG=10, Contribute=102}
The Value associated to Geeks is : 100
The Value associated to Contribute is : 102

參考： https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ConcurrentHashMap.html#get()

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注：本文由純淨天空篩選整理自RICHIK BHATTACHARJEE大神的英文原創作品 ConcurrentHashMap get() 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。