如何在Java中使ArrayList只读？

╰半夏微凉° 2023-03-05 12:51 14阅读 0赞

## 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][https_www.includehelp.com_java_make-arraylist-read-only-in-java.aspx]

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