Java uses the containsKey() function of the Hashtable class to determine whether the collection contains the specified key.

Java uses the containsKey() function of the Hashtable class to determine whether the set contains the specified key

In Java programming, the Hashtable class is a commonly used data structure used to store key-value pairs. It provides many convenient methods to manipulate and query the data in the collection. It contains a very useful method containsKey(), which is used to determine whether the specified key is included in the collection. This article will introduce how to use the containsKey() function of the Hashtable class and give corresponding code examples.

First of all, we need to understand the basic concepts and usage of the Hashtable class. Hashtable is a hash table, which inherits from the Dictionary class and implements the Map interface. Its characteristic is that the corresponding value can be quickly found by key. In Hashtable, both keys and values ​​must be of object type, and keys cannot be repeated and values ​​can be repeated.

The following is a simple Hashtable sample code:

import java.util.Hashtable;

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

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

        // 使用containsKey()函数判断集合中是否包含指定的键
        System.out.println(hashtable.containsKey("apple"));   // 输出：true
        System.out.println(hashtable.containsKey("pear"));    // 输出：false
    }
}

In the above code, we first create a Hashtable object and add three key-value pairs using the put() method. Then, we use the containsKey() function to determine whether the specified key is included in the collection. Here, we determine whether the keys "apple" and "pear" exist in the Hashtable, and the results output true and false respectively.

containsKey() function is an instance method of the Hashtable class. Its function is to determine whether the set contains the specified key. Returns true if the key is contained in the collection; false otherwise.

Use the containsKey() function to conveniently perform key search operations. It can help us avoid traversing the entire collection to find a certain key, improving the execution efficiency of the code.

Summary:
This article introduces the use of the containsKey() function of the Hashtable class in Java to determine whether the set contains the specified key. We learned the basic concepts and usage of the Hashtable class, and gave corresponding code examples. I hope this article will help you use the Hashtable class to perform key query operations in Java programming.

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