Java中的ConcurrentHashMap get()方法

Java .util.concurrent.ConcurrentHashMap 的get()方法是Java中的一个内置函数，它接受一个键作为参数并返回映射到它的值。如果作为参数传递的键不存在映射，则返回 null。

句法：

Concurrent.get(Object key_element)

参数：该方法接受对象类型的单个参数key_element ，它指的是应该返回其关联值的键。

返回值：该方法返回与参数中的key_element关联的值。

异常：当指定的key_element为 null 时，函数会抛出NullPointerException 。

下面的程序说明了Java.util.concurrent.ConcurrentHashMap.get()方法的使用：

程序 1：该程序涉及将字符串值映射到整数键。

// Java Program Demonstrate get()
// method of ConcurrentHashMap
  
import java.util.concurrent.*;
  
class GFG {
    public static void main(String[] args)
    {
  
        ConcurrentHashMap
            chm = new ConcurrentHashMap();
  
        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));
    }
}

输出：

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

程序 2：该程序涉及将整数值映射到字符串键。

// Java Program Demonstrate get()
// method of ConcurrentHashMap
  
import java.util.concurrent.*;
  
class GFG {
    public static void main(String[] args)
    {
  
        ConcurrentHashMap
            chm = new ConcurrentHashMap();
  
        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"));
    }
}

输出：

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

参考： https: Java/util/concurrent/ConcurrentHashMap.html#get()