Java中的字典 put() 方法及示例

Dictionary 的 put() 方法用于将映射插入到字典中。这意味着可以将特定的键与值一起映射到特定的字典中。

句法：

DICTIONARY.put(key, value)

参数：该方法有两个参数，都是 Dictionary 的 Object 类型。

• key：这是指需要插入到字典中进行映射的关键元素。
• value：这是指上述键将映射到的值。

返回值：该方法返回键映射到的值。如果键未映射到任何值，则返回 NULL。

下面的程序用于说明Java.util.Dictionary.put() 方法的工作：
方案一：

// Java code to illustrate the put() method
import java.util.*;
  
public class Dictionary_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty Dictionary
        Dictionary dict
            = new Hashtable();
  
        // Inserting values into the Dictionary
        dict.put(10, "Geeks");
        dict.put(15, "4");
        dict.put(20, "Geeks");
        dict.put(25, "Welcomes");
        dict.put(30, "You");
  
        // Displaying the Dictionary
        System.out.println("Initial Dictionary is: " + dict);
  
        // Inserting existing key along with new value
        String returned_value = (String)dict.put(20, "All");
  
        // Verifying the returned value
        System.out.println("Returned value is: " + returned_value);
  
        // Displaying the new table
        System.out.println("New Dictionary is: " + dict);
    }
}

输出：

Initial Dictionary is: {10=Geeks, 20=Geeks, 30=You, 15=4, 25=Welcomes}
Returned value is: Geeks
New Dictionary is: {10=Geeks, 20=All, 30=You, 15=4, 25=Welcomes}

方案二：

// Java code to illustrate the put() method
import java.util.*;
  
public class Dictionary_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty Dictionary
        Dictionary dict
            = new Hashtable();
  
        // Inserting values into the Dictionary
        dict.put(10, "Geeks");
        dict.put(15, "4");
        dict.put(20, "Geeks");
        dict.put(25, "Welcomes");
        dict.put(30, "You");
  
        // Displaying the Dictionary
        System.out.println("Initial Dictionary is: " + dict);
  
        // Inserting existing key along with new value
        String returned_value = (String)dict.put(50, "All");
  
        // Verifying the returned value
        System.out.println("Returned value is: " + returned_value);
  
        // Displaying the new table
        System.out.println("New Dictionary is: " + dict);
    }
}

输出：

Initial Dictionary is: {10=Geeks, 20=Geeks, 30=You, 15=4, 25=Welcomes}
Returned value is: null
New Dictionary is: {10=Geeks, 20=Geeks, 30=You, 50=All, 15=4, 25=Welcomes}