Java 中的 Collections checkedCollection()方法，带示例
原文:https://www . geeksforgeeks . org/collections-checked collection-method-in-Java-with-examples/
java.util.Collections 类的 checkedCollection() 方法用于返回指定集合的动态类型安全视图。返回的集合不会将 hashCode 和 equals 操作传递给后备集合，而是依赖于 Object 的 equals 和 hashCode 方法。在后备集合是集合或列表的情况下，这对于保留这些操作的契约是必要的。如果指定的集合可序列化，则返回的集合将是可序列化的。
因为 null 被认为是任何引用类型的值，所以每当后备集合插入 null 元素时，返回的集合都允许插入 null 元素。
语法:
public static Collection
checkedCollection(Collection c, Class type)
参数:该方法取两个参数
- 要为其返回动态类型安全视图的集合
- 允许 c 持有的元素类型
返回类型:该方法动态返回指定集合的类型安全视图
例 1:
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to demonstrate
// checkedCollection() method
// for String value
// Importing utility classes
import java.util.*;
// Main class
public class GFG {
// Main driver method
public static void main(String[] argv) throws Exception
{
// Try block to check for exceptions
try {
// Creating an empty ArrayList by
// creating object of List of string type
List<String> arlst = new ArrayList<String>();
// Adding element to arrlist
// using add() method
// Custom input elements
arlst.add("CSS");
arlst.add("PHP");
arlst.add("HTML");
arlst.add("TajMahal");
// Printing the ArrayList
System.out.println("List: " + arlst);
// Now create typesafe view of the collection bu
// creating object of Collection class of string
// type
Collection<String> tslst
= Collections.checkedCollection(
arlst, String.class);
// Printing the updated ArrayList
// after applying checkedCollection() method
System.out.println("Typesafe view of List: "
+ tslst);
}
// Catch block to handle the exceptions
catch (IllegalArgumentException e) {
// Print message to be displayed on console
// when exception occurs
System.out.println("Exception thrown : " + e);
}
}
}
Output:
List: [CSS, PHP, HTML, TajMahal]
Typesafe view of List: [CSS, PHP, HTML, TajMahal]
例 2:
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to Illustrate checkedCollection() method
// of Collection class for an Integer value
// Importing classes
import java.util.*;
// Main class
public class GFG {
// Main driver method
public static void main(String[] argv) throws Exception
{
// Try block to check for exception
try {
// Creating an empty ArrayList of integer type
// by declaring object of List
List<Integer> arlst = new ArrayList<Integer>();
// Adding element to ArrayList
// using add() method
arlst.add(20);
arlst.add(30);
arlst.add(40);
arlst.add(50);
// Printing the above ArrayList
System.out.println("List: " + arlst);
// now creating typesafe view of the collection
// using checkedCollection() method
Collection<Integer> tslst
= Collections.checkedCollection(
arlst, Integer.class);
// Printing the updated ArrayList
// after above operation
System.out.println("Typesafe view of List: "
+ tslst);
}
// Catch block to handle exceptions
catch (IllegalArgumentException e) {
// Display message if exception occurs
System.out.println("Exception thrown : " + e);
}
}
}
Output:
List: [20, 30, 40, 50]
Typesafe view of List: [20, 30, 40, 50]
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