Java中的集合checkedList()方法和示例

Collections 类的checkedList()方法存在于Java.util 包中，用于返回指定列表的动态类型安全视图。这里要注意的关键是，如果指定的列表是可序列化的，则返回的列表将是可序列化的。由于 null 被认为是任何引用类型的值，因此返回的列表允许在后备列表中插入 null 元素。

Tip: This method is compatiable with java version 1.5 and onwards.

句法：

public static  List
checkedList(List list, Class type)

参数：此方法采用以下参数作为参数：

• 要为其返回动态类型安全视图的列表
• 列表允许持有的元素类型

返回类型：指定列表的动态类型安全视图。

异常：此方法抛出ClassCastException

示例 1：

Java

// Java program to Demonstrate checkedList() method
// of Collections class for a string value
 
// Importing required 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 ArrayList of string type by
            // declaring object of List
            List arlst = new ArrayList();
 
            // Adding element to ArrayList
            // by using standard add() method
 
            // Custom input elements
            arlst.add("A");
            arlst.add("B");
            arlst.add("C");
            arlst.add("TajMahal");
 
            // Printing the above elements inside ArrayList
            System.out.println("List: " + arlst);
 
            // Creating typesafe view of the specified list
            // and applying checkedList
            List tslst = Collections.checkedList(
                arlst, String.class);
 
            // Printing the updated elements of ArrayList
            // after applying above operation
            System.out.println("Typesafe view of List: "
                               + tslst);
        }
 
        // Catch block to handle the exceptions
        catch (IllegalArgumentException e) {
 
            // Display message on console if exception
            // occurs
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

List: [A, B, C, TajMahal]
Typesafe view of List: [A, B, C, TajMahal]

示例 2：

Java

// Java program to Demonstrate checkedList() method
// of Collections class for a string value
 
// Importing required 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 of integer type
            // by creating an object of List
            List arlst = new ArrayList();
 
            // Adding element to above ArrayList
            // by using add() method
            arlst.add(20);
            arlst.add(30);
            arlst.add(40);
            arlst.add(50);
 
            // Printing the elements of above ArrayList
            System.out.println("List: " + arlst);
 
            // Creating typesafe view of the specified list
            // with usage of checkedList() method
            List tslst = Collections.checkedList(
                arlst, Integer.class);
 
            // Printing the elements of ArrayList
            // after performing above operation
            System.out.println("Typesafe view of List: "
                               + tslst);
        }
 
        // Catch block to handle the exceptions
        catch (IllegalArgumentException e) {
 
            // Display message if exception occurs
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出：

List: [20, 30, 40, 50]
Typesafe view of List: [20, 30, 40, 50]