集合类singletonMap()方法 (Collections Class singletonMap() method)

• singletonMap() method is available in java.util package.

  singletonMap()方法在java.util包中可用。

• singletonMap() method is used to return an immutable map (i.e. immutable map is a map that contains the given key & value only & mapping would be based on the given key to the given value.

  singletonMap()方法用于返回不可变的映射(即，不可变的映射是仅包含给定键和值的映射，并且映射将基于给定键到给定值。

• singletonMap() method is a static method, so it is accessible with the class name and if we try to access the method with the class object then we will not get an error.

  singletonMap()方法是静态方法，因此可以使用类名进行访问，如果尝试使用类对象访问该方法，则不会收到错误。

• singletonMap() method does not throw an exception at the time of returning an immutable map.

  在返回不可变地图时， singletonMap()方法不会引发异常。

Syntax:

句法：

    public static Map singletonMap(Type key_ele, Type val_ele);

Parameter(s):

参数：

• Type key_ele – represents the key to be saved in the returned map.

  key_ele类型 –表示要保存在返回的映射中的密钥。

• Type val_ele – represents the value(val) associated with the key_ele.

  类型val_ele –表示与key_ele关联的value( val )。

Return value:

返回值：

The return type of this method is Map, it returns an immutable map that contains the given key-value pairs only of the map.

此方法的返回类型为Map ，它返回一个不可变的映射，其中仅包含该映射的给定键值对。

Example:

例：

// Java program is to demonstrate the example of
// singletonMap(Type key_ele, Type val_ele)
// method of Collections
import java.util.*;
public class SingletonMapOfCollections {
public static void main(String args[]) {
// Instatiates a hash map object
Map < Integer, String > map = new HashMap < Integer, String > ();
// By using put() method is to add
// objects in a hash map
map.put(10, "C");
map.put(20, "C++");
map.put(30, "JAVA");
map.put(40, "C");
map.put(50, "C++");
// Display Map
System.out.println("Map: " + map);
// By using singletonMap() method is to
// list the given key-value pair only
map = Collections.singletonMap(30, "JAVA");
// Display SingletonMap
System.out.println("Collections.singletonMap(30,JAVA): " + map);
}
}

Output

输出量

Map: {50=C++, 20=C++, 40=C, 10=C, 30=JAVA}
Collections.singletonMap(30,JAVA): {30=JAVA}

翻译自: https://www.includehelp.com/java/collections-singletonmap-method-with-example.aspx