Use the get() method of the HashMap class in Java to obtain the value corresponding to the key

Use the get() method of the HashMap class in Java to obtain the value corresponding to the key

In Java programming, HashMap is a commonly used data structure used to store key-value pairs in a one-to-one mapping relationship . HashMap allows us to quickly access values ​​by key and has good performance.

The HashMap class provides many methods, one of which is the get() method, which is commonly used to obtain the value corresponding to the key. Below we will introduce how to use the get() method of the HashMap class and provide sample code for demonstration.

First, we need to create a HashMap object and add some key-value pairs. Here we use the generic type of HashMap, specifying the key type as String and the value type as Integer.

import java.util.HashMap;

public class HashMapExample {
    public static void main(String[] args) {
        // 创建一个HashMap对象
        HashMap<String, Integer> hashMap = new HashMap<>();

        // 添加键值对
        hashMap.put("apple", 1);
        hashMap.put("banana", 2);
        hashMap.put("orange", 3);
        hashMap.put("grape", 4);

        // 使用get()方法获取键对应的值
        int value = hashMap.get("banana");
        System.out.println("键 'banana' 对应的值为：" + value);
    }
}

In the above code, we first created a HashMap object and added four sets of key-value pairs through the put() method. Then, we use the get() method to get the value corresponding to the key "banana" and assign it to the variable value. Finally, by printing the output, we can see that the key "banana" corresponds to a value of 2.

It should be noted that when we use the get() method to obtain the value corresponding to the key, if the key does not exist in the HashMap, the get() method will return null. In order to avoid null pointer exceptions, we can use the containsKey() method to determine whether the key exists in the HashMap before using the get() method.

The following is a sample code using the containsKey() method:

import java.util.HashMap;

public class HashMapExample {
    public static void main(String[] args) {
        // 创建一个HashMap对象
        HashMap<String, Integer> hashMap = new HashMap<>();

        // 添加键值对
        hashMap.put("apple", 1);
        hashMap.put("banana", 2);
        hashMap.put("orange", 3);
        hashMap.put("grape", 4);

        // 使用containsKey()方法判断HashMap中是否存在某个键
        if (hashMap.containsKey("banana")) {
            int value = hashMap.get("banana");
            System.out.println("键 'banana' 对应的值为：" + value);
        } else {
            System.out.println("HashMap中不存在键 'banana'");
        }
    }
}

In the above code, we use the containsKey() method to determine whether the key "banana" exists in the HashMap. If it exists, the corresponding value is obtained and printed; if it does not exist, a prompt message is output.

Through the above example, we can simply understand how to use the get() method of the HashMap class to obtain the value corresponding to the key. In actual development, the get() method of HashMap is very practical when querying and obtaining values, which can greatly improve the efficiency and readability of the code.

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