Java Collections emptyList()
Java集合类的
emptyList()方法用于获取没有元素的List。这些空列表本质上是不可变的。
语法
以下是
emptyList()方法的声明:
public static final <T> List<T> emptyList()
参数
此方法不接受任何参数。
返回
emptyList()方法返回一个空的不可变列表。
例外
NA
兼容版本
Java 1.5及更高版本
示例1
import java.util.*;
public class CollectionsEmptyListExample1 {
public static void main(String[] args) {
//Create an empty List
List<String> EmptyList = Collections.<String>emptyList();
System.out.println("Empty list: "+EmptyList);
}
}
输出:
示例2
import java.util.*;
public class CollectionsEmptyListExample2 {
public static void main(String[] args) {
//Create an empty List
List<String> emptylist = Collections.emptyList();
System.out.println("Created empty immutable list: "+emptylist);
//try to add elements
emptylist.add("A");
emptylist.add("B");
}
}
输出:
Created empty immutable list: []
Exception in thread "main" java.lang.UnsupportedOperationException
at java.base/java.util.AbstractList.add(AbstractList.java:153)
at java.base/java.util.AbstractList.add(AbstractList.java:111)
at myPackage.CollectionsEmptyListExample1.main(CollectionsEmptyListExample1.java:9)
示例3
import java.util.*;
public class CollectionsEmptyListExample3 {
public static void main(String[] args) {
//Create an empty List
List<Integer> empList = Collections.emptyList();
empList.add(1);
empList.add(2);
System.out.println("Created empty immutable List: "+empList);
}
}
输出:
Exception in thread "main" java.lang.UnsupportedOperationException
at java.base/java.util.AbstractList.add(AbstractList.java:153)
at java.base/java.util.AbstractList.add(AbstractList.java:111)
at myPackage.CollectionsEmptyListExample3.main(CollectionsEmptyListExample3.java:8)
