Java中的集合checkedMap()方法和示例

Collections 类的checkedMap()方法存在于Java.util 包中，用于返回指定映射的动态类型安全视图。如果指定的映射是可序列化的，则返回的映射将是可序列化的。由于 null 被认为是任何引用类型的值，因此返回的映射允许在支持映射时插入空键或值。

句法：

public static  Map 
checkedMap(Map m, Class keyType, Class valueType)

参数：此方法采用以下 3 个参数作为参数，如下所列：

• 要为其返回动态类型安全视图的映射
• 允许 m 持有的密钥类型
• m 被允许持有的值的类型

返回值：此方法返回指定映射的动态类型安全视图。

异常：此方法确实抛出 ClassCastException

Tip: This method is compatible with java version 1.5 and onwards.

现在让我们看几个例子，以实现上述方法并更好地理解该方法，如下所示：

示例 1：

Java

// Java program to Demonstrate checkedMap() method
// of Collections class
 
// Importing required classes
import java.util.*;
 
// Main class
public class GFG {
 
    // Main driver method
    public static void main(String[] argv) throws Exception
    {
 
        // Try block to check for exceptions
        try {
 
            // Creating an empty HashMap by declaring
            // HashMap key-value pairs
            //  of string and string type
            HashMap hmap
                = new HashMap();
 
            // Adding custom key-value pairs to above
            // HashMap
            hmap.put("Ram", "Shyam");
            hmap.put("Karan", "Arjun");
            hmap.put("Karn", "Veer");
            hmap.put("duryodhan", "dhrupat");
 
            // Printing all the key-value pairs of above
            // HashMap
            System.out.println("Map: \n" + hmap);
 
            // Now creating typesafe view of the specified
            // map using checkedMap() method of Collections
            // class
            Map tsmap
                = Collections.checkedMap(hmap, String.class,
                                         String.class);
 
            // Now printing the typesafe view of specified
            // list
            System.out.println("Typesafe view of Map: "
                               + tsmap);
        }
 
        // Catch block to handle the exceptions
        catch (IllegalArgumentException e) {
 
            // Display message when exception occurs
            System.out.println("Exception thrown : \n" + e);
        }
    }
}

输出：

Map: 
{Karn=Veer, Karan=Arjun, duryodhan=dhrupat, Ram=Shyam}
Typesafe view of Map: 
{Karn=Veer, Karan=Arjun, duryodhan=dhrupat, Ram=Shyam}

示例 2：

Java

// Java program to demonstrate checkedMap() method
// of Collections class
 
// Importing all required classes
import java.util.*;
 
// Main class
public class GFG {
 
    // Main driver method
    public static void main(String[] argv) throws Exception
    {
 
        // Try block to check for exceptions
        try {
 
            // Creating an empty HashMap by
            // declaring object of string and integer type
            HashMap hmap
                = new HashMap();
 
            // Adding key-value pairs to above HashMap
            // object
            hmap.put("Player-1", 20);
            hmap.put("Player-2", 30);
            hmap.put("Player-3", 40);
 
            // Printing the elements inside above HashMap
            // object
            System.out.println("Map: \n" + hmap);
 
            // Now creating typesafe view of the specified
            // map using checkedMap() method
            Map tsmap
                = Collections.checkedMap(hmap, String.class,
                                         Integer.class);
 
            // Again printing the typesafe view of specified
            // list
            System.out.println("Typesafe view of Map: \n"
                               + tsmap);
        }
 
        // Catch block to handle exceptions
        catch (IllegalArgumentException e) {
 
            // Display message when exception occurs
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

Map: 
{Player-1=20, Player-3=40, Player-2=30}
Typesafe view of Map: 
{Player-1=20, Player-3=40, Player-2=30}