使ArrayList只读 (Making ArrayList Read-Only)

Given an ArrayList, and we have to make it Read-Only in Java.

给定一个ArrayList，我们必须使其成为Java只读。

Read-Only: If we make ArrayList as Read-Only i.e. we can only read ArrayList and we cannot perform other operations on ArrayList like delete, replace, add by using remove(), set(), add() methods, in read-only mode or in other words we cannot perform any modification in the ArrayList during Read-Only mode.

只读：如果我们将ArrayList设为只读，即我们只能读取ArrayList，则无法在ArrayList上执行其他操作，如delete，replace，add(使用remove()，set()，add()方法)，如read-只读模式，换句话说，我们不能在只读模式下对ArrayList进行任何修改。

To make an ArrayList read-only, we use unmodifiableCollection() method of the Collections class.

为了使ArrayList为只读，我们使用Collections类的unmodifiableCollection()方法 。

unmodifiableCollection() method

unmodifiableCollection()方法

• unmodifiableCollection() method is available in java.util package.

  unmodifiableCollection()方法在java.util包中可用。

• unmodifiableCollection() method is used to make java collections (ArrayList) read-only.

  unmodifiableCollection()方法用于将Java集合(ArrayList)设为只读。

• unmodifiableCollection() method is used to returns the same ArrayList as we input (i.e. unmodifiable view).

  unmodifiableCollection()方法用于返回与我们输入相同的ArrayList(即，不可修改的视图)。

• unmodifiableCollection() method may throw an exception at the time of modification in unmodifiableCollection view.

  在unmodifiableCollection视图中进行修改时， unmodifiableCollection()方法可能会引发异常。

  UnsupportedOperationException: In this exception, if we attempt to modify the collection.

  UnsupportedOperationException：在此异常中，如果我们尝试修改集合。

Syntax:

句法：

    public static Collection unmodifiableCollection(Collection co){
}

Parameter(s):

参数：

co –represents the ArrayList collection object for which an unmodifiable view is to be returned.

共 -代表的ArrayList集合对象一个不可修改视图将被返回。

Return value:

返回值：

The return type of this method is Collection, it returns an unmodifiable view of the collection.

此方法的返回类型为Collection ，它返回该集合的不可修改视图。

Example:

例：

// Java program to demonstrate the example of 
// Java ArrayList make Read-Only by using 
// unmodifiableCollection() method of Collections class
import java.util.*;
public class ArrayListMakeReadOnly {
public static void main(String[] args) {
// ArrayList Declaration
Collection arr_list = new ArrayList();
// By using add() method to add few elements in 
// ArrayList
arr_list.add(10);
arr_list.add(20);
arr_list.add(30);
arr_list.add(40);
arr_list.add(50);
// Display ArrayList 
System.out.println("Display ArrayList Elements");
System.out.println(arr_list);
System.out.println();
// By using unmodifiableCollection() method is used to make 
// ArrayList Read-Only
Collection al_ro = Collections.unmodifiableCollection(arr_list);
// We will get an exception if we add element in Read-Only 
// ArrayList i.e. Below statement is invalid
// al_ro.add(60); 
// We will get an exception if we delete element from Read-Only 
// ArrayList i.e. Below statement is invalid
// al_ro.remove(1); 
// We will get an exception if we replace element in Read-Only 
// ArrayList i.e. Below statement is invalid
// al_ro.set(2,60); 
}
}

Output

输出量

Display ArrayList Elements
[10, 20, 30, 40, 50]

翻译自: https://www.includehelp.com/java/make-arraylist-read-only-in-java.aspx