Java Collections unmodifiableCollection()
Java集合类的
unmodifiableCollection()方法用于获取不可修改的指定集合的视图。如果尝试直接或通过其迭代器修改返回的集合，则将导致UnsupportedOperationException。
语法
以下是
unmodifiableCollection()方法的声明:
public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c)
参数
| 参数 |
说明 |
必需/可选 |
| c |
这是要返回不可修改视图的集合。 |
必需 |
返回
unmodifiableCollection()方法返回指定集合的不可修改视图。
异常
不适用
示例1
import java.util.*;
public class CollectionsUnmodifiableCollectionExample1 {
public static void main(String[] args) {
Collection<String> c = new ArrayList<>();
Collections.addAll(c, "Google", "Mozila FireFox", "Yahoo");
Collection<String> c2 = Collections.unmodifiableCollection(c);
System.out.println("Unmodifiable Collection: " + c2);
c.add("Safari");
System.out.println("Unmodifiable Collection after adding element to the original one:");
System.out.println(c2);
}
}
输出:
Unmodifiable Collection: [Google, Mozila FireFox, Yahoo]
Unmodifiable Collection after adding element to the original one:
[Google, Mozila FireFox, Yahoo, Safari]
示例2
import java.util.*;
public class CollectionsUnmodifiableCollectionExample2 {
public static void main(String[] args) {
Collection<String> c = new ArrayList<>();
Collections.addAll(c, "Google", "Mozila FireFox", "Yahoo");
System.out.println("Initial Collection: "+ c);
Collection<String> c2 = Collections.unmodifiableCollection(c);
c2.add("Safari");
}
}
输出:
Initial Collection: [Google, Mozila FireFox, Yahoo]
Exception in thread "main" java.lang.UnsupportedOperationException
at java.base/java.util.Collections$UnmodifiableCollection.add(Collections.java:1056)
at myPackage.UnmodifiableCollectionExample2.main(UnmodifiableCollectionExample2.java:9)
示例3
import java.util.*;
public class CollectionsUnmodifiableCollectionExample3 {
public static void main(String[] args) {
Collection<Integer> coll = new ArrayList<>();
coll.add(10);
coll.add(20);
coll.add(30);
coll.add(40);
Collection<Integer> coll2 = Collections.unmodifiableCollection(coll);
System.out.println("Unmodifiable collection: " + coll2);
coll.add(50);
System.out.print("Unmodifiable collection after adding (50): "+coll);
}
}
输出:
Unmodifiable collection: [10, 20, 30, 40]
Unmodifiable collection after adding (50): [10, 20, 30, 40, 50]
