Java Collections unmodifiableList()
Java集合类的
unmodifiableList()方法用于获取不可修改的指定列表的视图。如果尝试直接或通过其迭代器修改返回的列表，则会导致UnsupportedOperationException。
语法
以下是
unmodifiableList的声明()方法:
public static <T> List<T> unmodifiableList(List<? extends T> list)
参数
| 参数 |
说明 |
必需/可选 |
| list |
这是要返回不可修改视图的列表。 |
必需 |
返回
unmodifiableList()方法返回指定列表的不可修改视图。
异常
不适用
示例1
import java.util.*;
public class CollectionsUnmodifiableListExample1 {
public static void main(String[] args) {
List<String> list = new ArrayList<>();
Collections.addAll(list, "Google", "Mozila FireFox", "Yahoo");
List<String> list2 = Collections.unmodifiableList(list);
System.out.println("Unmodifiable List: " + list2);
list.add("Safari");
System.out.print("Unmodifiable List after adding element to the list:");
System.out.println(list2);
}
}
输出:
Unmodifiable List: [Google, Mozila FireFox, Yahoo]
Unmodifiable List after adding element to the list:[Google, Mozila FireFox, Yahoo, Safari]
示例2
import java.util.*;
public class CollectionsUnmodifiableListExample2 {
public static void main(String[] args) {
List<String> list = new ArrayList<>();
Collections.addAll(list, "Google", "Mozila FireFox", "Yahoo");
List<String> list2 = Collections.unmodifiableList(list);
System.out.println("Unmodifiable List: " + list2);
list2.add("Safari");
}
}
输出:
Unmodifiable List: [Google, Mozila FireFox, Yahoo]
Exception in thread "main" java.lang.UnsupportedOperationException
at java.base/java.util.Collections$UnmodifiableCollection.add(Collections.java:1056)
at myPackage.UnmodifiableListExample2.main(UnmodifiableListExample2.java:9)
示例3
import java.util.*;
public class CollectionsUnmodifiableListExample3 {
public static void main(String[] args) {
ArrayList<Integer> list = new ArrayList<>();
list.add(10);
list.add(20);
list.add(30);
list.add(40);
List<Integer> list2 = Collections.unmodifiableList(list);
System.out.println("Unmodifiable list: " + list2);
list.add(50);
System.out.println("Unmodifiable list after adding (50): "+list);
}
}
输出:
Unmodifiable list: [10, 20, 30, 40]
Unmodifiable list after adding (50): [10, 20, 30, 40, 50]
