Java Collections emptyMap()
Java Collections 类的
emptyMap()方法返回一个不变的空映射。
语法
以下是
emptyMap()方法的声明:
public static final <K,V> Map<K,V> emptyMap()
参数
此方法不接受任何参数。
返回
空映射()方法返回一个空的不变Map。
异常
NA
兼容版本
Java 1.5及更高版本
示例1
import java.util.*;
public class CollectionsEmptyMapExample1 {
public static void main(String[] args) {
//Create an empty Map
Map<String,String> EmptyMap = Collections.emptyMap</span>();
System.out.println("Created Empty Map: "+EmptyMap);
}
}
输出:
示例2
import java.util.*;
public class CollectionsEmptyMapExample2 {
public static void main(String[] args) {
//Create an empty Map
Map<String,String> EmptyMap = Collections.emptyMap</span>();
System.out.println("Created Empty Map: "+EmptyMap);
// try to add elements
EmptyMap.put("1","from lidihuo.com");
}
}
输出:
Created Empty Map: {}
Exception in thread "main" java.lang.UnsupportedOperationException
at java.base/java.util.AbstractMap.put(AbstractMap.java:209)
at myPackage.CollectionsEmptyMapExample2.main(CollectionsEmptyMapExample2.java:9)
示例3
import java.util.*;
public class CollectionsEmptyMapExample3 {
public static void main(String[] args) {
//Create an empty Map
Map<Integer, Integer> empMap = Collections.emptyMap</span>();
empMap.put(1, 23424);
empMap.put(2, 65776);
System.out.println("Created empty immutable Map: "+empMap);
}
}
输出:
Exception in thread "main" java.lang.UnsupportedOperationException
at java.base/java.util.AbstractMap.put(AbstractMap.java:209)
at myPackage.CollectionsEmptyMapExample3.main(CollectionsEmptyMapExample3.java:7)