Using the size() method of the Hashtable class in Java to obtain the number of key-value pairs in the hash table

Use the size() method of the Hashtable class in Java to obtain the number of key-value pairs in the hash table

The hash table (Hashtable) is a key-value pair storage structure that uses a hash function to convert keys Maps to storage locations for efficient data lookup. In Java, Hashtable is a thread-safe hash table implementation class that provides rich operation methods and properties.

The size() method in the Hashtable class can be used to obtain the number of key-value pairs in the hash table. Below we will show you how to use this method with a code example.

First of all, before using the Hashtable class in Java, you need to import the java.util package so that you can use the Hashtable class.

import java.util.Hashtable;

Next, we create a Hashtable object and add some key-value pairs to it.

Hashtable<String, Integer> hashtable = new Hashtable<>();

hashtable.put("张三", 25);
hashtable.put("李四", 30);
hashtable.put("王五", 35);

After adding three key-value pairs, we can use the size() method to get the number of key-value pairs in the hash table.

int size = hashtable.size();
System.out.println("哈希表中键值对的数量为：" + size);

Run the above code, the output result is as follows:

哈希表中键值对的数量为：3

As you can see, we used the size() method of the Hashtable class to successfully obtain the number of key-value pairs in the hash table.

It should be noted that the size() method of the Hashtable class returns the number of key-value pairs in the hash table, not the number of keys or values. Therefore, if there are two keys corresponding to the same value, the value returned by the size() method is still 1.

In addition, it should be noted that the Hashtable class is a thread-safe class, so it is safe to operate in a multi-threaded environment. If you need to operate a hash table in a multi-threaded environment, you can use the Hashtable class to ensure data security.

In actual development, we often need to obtain the number of key-value pairs in the hash table to perform related operations, such as determining whether the hash table is empty, or checking whether a certain key exists in the hash table. With the help of the size() method of the Hashtable class, we can easily obtain the number of key-value pairs in the hash table, thus helping us better manage and manipulate the hash table.

To sum up, this article introduces how to use the size() method of the Hashtable class in Java to obtain the number of key-value pairs in the hash table. Through the sample code in this article, I hope readers can better understand the usage of this method and its application scenarios in actual development.

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