java Java 中的 ConcurrentHashMap get()方法

Java 中的 ConcurrentHashMap get()方法

原文:https://www . geesforgeks . org/concurrenthashmap-get-method-in-Java/

java . util . 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。

语法:

Concurrent.get(Object key_element)

参数:该方法接受对象类型的单个参数 key_element ，该参数是指其关联值应该被返回的键。

返回值:该方法返回与参数中键 _ 元素相关联的值。

异常:当指定的 key_element 为空时，函数抛出 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<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));
    }
}

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<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"));
    }
}

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