Use the put() method of the Hashtable class to insert key-value pairs into the Hashtable

Hashtable is a data structure class in Java, used to store key-value pairs. It is based on the implementation of hash table and can efficiently perform insertion, search and deletion operations of elements. In the Hashtable class, the method for inserting key-value pairs is the put() method.

The put() method is used to insert the specified key-value pair into the Hashtable. It accepts two parameters. The first parameter is the key, which is used to uniquely identify a value; the second parameter is the value, which is the data to be stored. The following is a code example for inserting key-value pairs using the put() method of the Hashtable class:

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<>();

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

        // 输出Hashtable中的键值对
        System.out.println(hashtable);
    }
}

In the above code, a Hashtable object is first created. Notice that when creating a Hashtable object, we use generics to specify the key and value types. Here we specify that the key type is String and the value type is Integer.

Then, by calling the put() method, we insert the three key-value pairs into the Hashtable in sequence. The keys are "apple", "banana" and "orange", and the corresponding values ​​are 1, 2 and 3 respectively.

Finally, we use the System.out.println() method to output the key-value pairs in the Hashtable. Running the above code, the output result is as follows:

{orange=3, apple=1, banana=2}

As you can see, the output result is a Hashtable expressed in the form of key-value pairs. The key-value pairs in the Hashtable are unordered, but the order inserted through the put() method will be preserved.

In addition to using the put() method to insert key-value pairs into the Hashtable, you can also use the putIfAbsent() method to insert key-value pairs. The putIfAbsent() method will first determine whether the specified key already exists when inserting, and will insert it only if it does not exist.

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<>();

        // 插入键值对
        hashtable.putIfAbsent("apple", 1);
        hashtable.putIfAbsent("banana", 2);
        hashtable.putIfAbsent("orange", 3);
        hashtable.putIfAbsent("apple", 4);

        // 输出Hashtable中的键值对
        System.out.println(hashtable);
    }
}

In the above code, we use the putIfAbsent() method to insert four key-value pairs, one of which is the key "apple". Run the code and the output is as follows:

{orange=3, apple=1, banana=2}

You can see that when inserting a key-value pair with the key "apple", the insertion operation will not be performed because the same key already exists.

To summarize, key-value pairs can be inserted into a Hashtable using the put() method of the Hashtable class. If you want to ensure that the inserted key does not exist, you can use the putIfAbsent() method to insert it. Either way, the inserted key-value pairs will remain in the Hashtable in the order they were inserted.

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