Interpretation of Java documentation: Detailed explanation of usage of containsKey() method of HashMap class

Java document interpretation: Detailed explanation of the usage of the containsKey() method of the HashMap class, specific code examples are required

Introduction:
HashMap is a commonly used data in Java structure, which provides efficient storage and search capabilities. The containsKey() method is used to determine whether the HashMap contains the specified key. This article will explain in detail how to use the containsKey() method of the HashMap class and provide specific code examples.

1. Definition of containsKey() method
containsKey(Object key) method is an instance method in the HashMap class. It is used to determine whether the HashMap contains the specified key, that is, to determine whether a specific key exists. key. The definition of this method is as follows:
boolean containsKey(Object key)

2. Parameters of containsKey() method
containsKey() method accepts a parameter of type Object, which is used to represent the object to be judged key value. HashMap can store any type of key-value pairs, so the parameters can be instance objects of any class.

3. Return value of containsKey() method
containsKey() method returns a boolean type value. If the HashMap contains the specified key, the return value is true; if the HashMap does not contain the specified key, the return value is The value is false.

4. Examples of 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<>();
    
    // 向HashMap中添加键值对
    hashMap.put("apple", 3);
    hashMap.put("banana", 5);
    hashMap.put("orange", 2);
    
    // 判断HashMap中是否包含指定的键
    boolean containsApple = hashMap.containsKey("apple");
    boolean containsGrape = hashMap.containsKey("grape");
    
    // 输出结果
    System.out.println(""apple" is in the HashMap: " + containsApple);
    System.out.println(""grape" is in the HashMap: " + containsGrape);
}

}

Run the above code, we will get the following output:

"apple" is in the HashMap: true
"grape" is in the HashMap: false

The above code is first created Create a HashMap object and use the put() method to add three sets of key-value pairs to the HashMap. Then, use the containsKey() method to determine whether the HashMap contains the specified key, and determine whether the "apple" and "grape" keys exist respectively. Finally, by printing the output, we can see that the "apple" key exists in the HashMap, but the "grape" key does not exist in the HashMap.

Summary:
Through the above code examples, we can understand the usage of the containsKey() method of the HashMap class. This method is used to determine whether the HashMap contains the specified key and returns a boolean value. In actual programming, we can perform corresponding business processing based on the return value of the containsKey() method.

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