Java Collections checkedList()
checkedList()是Java Collections 类的一种方法，该方法返回指定列表的动态类型安全视图。如果插入的元素类型错误，将立即导致ClassCastException。
语法
以下是
checkedList()方法的声明:
public static <E> List<E> checkedList(List<E> list, Class<E> type)
参数
| 参数 |
说明 |
必需/可选 |
| list |
这是要为其返回动态类型安全视图的列表。 |
必需 |
| type |
这是允许列表保存的元素的类型。 |
必需 |
返回
checkedList()方法返回指定列表的动态类型安全视图。
异常
ClassCastException
兼容版本
Java 1.5及更高版本
示例1
import java.util.*;
public class CollectionsCheckedListExample1 {
public static void main(String[] args) {
//Create list
ArrayList<String> arrlist = new ArrayList<String>();
arrlist.add("A");
arrlist.add("B");
arrlist.add("C");
arrlist.add("D");
//Create type safe view of the List
System.out.println("Type safe view of the List is: "+Collections.checkedList(arrlist,String.class));
}
}
输出:
Type safe view of the List is: [A, B, C, D]
示例2
import java.util.*;
public class CollectionsCheckedListExample2 {
public static void main(String[] args) {
List myList = new ArrayList();
myList.add("one");
myList.add("two");
myList.add("three");
myList.add("four");
List chkList = Collections.checkedList(myList, String.class);
System.out.println("Checked list content: "+chkList);
//you can add any type of elements to myList object
myList.add(10);
//you cannot add any type of elements to chkList object, doing so throws ClassCastException
chkList.add(10); //throws ClassCastException
}
}
输出:
Checked list content: [one, two, three, four]
Exception in thread "main" java.lang.ClassCastException: Attempt to insert class java.lang.Integer element into collection with element type class java.lang.String
at java.base/java.util.Collections$CheckedCollection.typeCheck(Collections.java:3038)
at java.base/java.util.Collections$CheckedCollection.add(Collections.java:3081)
at myPackage.CollectionCheckedListExample2.main(CollectionCheckedListExample2.java:15)
示例3
import java.util.*;
public class CollectionsCheckedListExample3 {
public static void main(String[] args) {
//Create list
ArrayList<Integer> arrlist = new ArrayList<Integer>();
arrlist.add(10);
arrlist.add(20);
arrlist.add(30);
arrlist.add(40);
//Create type safe view of the collection
Collection<Integer> tsafelist;
tsafelist = Collections.checkedList(arrlist,Integer.class);
System.out.println("Type safe view of the List is: "+tsafelist);
}
}
输出:
Type safe view of the List is: [10, 20, 30, 40]
示例4
import java.util.*;
public class CollectionsCheckedListExample4 {
public static void main(String[] args) {
List<String> list = new ArrayList<>();
list.add("RAJ");
System.out.println(list);
List list2 = list;
list2.add(2);
System.out.println(list2);
}
}
输出:
