Java Collections checkedMap()用法及代码示例

java.util.Collections类的checkedMap()方法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，只要有支持映射，返回的映射就允许插入null键或值。

用法:

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

参数：此方法将以下参数作为参数：

m –要为其返回动态类型安全视图的Map
keyType –m允许持有的 key 的类型
valueType –m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。

以下示例说明了checkedMap()方法

示例1:

// Java program to demonstrate 
// checkedMap() method 
// for <String, String> value 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) throws Exception 
    { 
  
        try { 
  
            // creating object of HashMap<String> 
            HashMap<String, String> 
                hmap = new HashMap<String, String>(); 
  
            // Adding elemnet to hmap 
            hmap.put("Ram", "Shyam"); 
            hmap.put("Karan", "Arjun"); 
            hmap.put("Karn", "Veer"); 
            hmap.put("duryodhan", "dhrupat"); 
  
            // printing the map 
            System.out.println("Map: \n" + hmap); 
  
            // create typesafe view of the specified map 
            // using checkedMap() method 
            Map<String, String> 
                tsmap = Collections 
                            .checkedMap(hmap, 
                                        String.class, 
                                        String.class); 
  
            // printing the typesafe view of specified list 
            System.out.println("Typesafe view of Map: " + tsmap); 
        } 
  
        catch (IllegalArgumentException e) { 
            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 program to demonstrate 
// checkedMap() method 
// for <String, Integer> value 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) 
        throws Exception 
    { 
  
        try { 
  
            // creating object of HashMap<String> 
            HashMap<String, Integer> 
                hmap = new HashMap<String, Integer>(); 
  
            // Adding elemnet to hmap 
            hmap.put("Player-1", 20); 
            hmap.put("Player-2", 30); 
            hmap.put("Player-3", 40); 
  
            // printing the map 
            System.out.println("Map: \n" + hmap); 
  
            // create typesafe view of the specified map 
            // using checkedMap() method 
            Map<String, Integer> 
                tsmap = Collections 
                            .checkedMap(hmap, String.class, Integer.class); 
  
            // printing the typesafe view of specified list 
            System.out.println("Typesafe view of Map: \n" + tsmap); 
        } 
  
        catch (IllegalArgumentException e) { 
            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}

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注：本文由纯净天空筛选整理自RohitPrasad3大神的英文原创作品 Collections checkedMap() method in Java with Examples。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。