使ArrayList只讀 (Making ArrayList Read-Only)

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

給定一個ArrayList，我們必須使其成為Java只讀。

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.

只讀：如果我們將ArrayList設為只讀，即我們只能讀取ArrayList，則無法在ArrayList上執行其他操作，如delete，replace，add(使用remove()，set()，add()方法)，如read-只讀模式，換句話說，我們不能在只讀模式下對ArrayList進行任何修改。

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

為了使ArrayList為只讀，我們使用Collections類的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()方法用于將Java集合(ArrayList)設為只讀。

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

  unmodifiableCollection()方法用于返回與我們輸入相同的ArrayList(即，不可修改的視圖)。

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

  在unmodifiableCollection視圖中進行修改時， unmodifiableCollection()方法可能會引發異常。

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

  UnsupportedOperationException：在此異常中，如果我們嘗試修改集合。

Syntax:

句法：

public static Collection unmodifiableCollection(Collection co){}

Parameter(s):

參數：

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

共 -代表的ArrayList集合對象一個不可修改視圖將被返回。

Return value:

返回值：

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

此方法的返回類型為Collection ，它返回該集合的不可修改視圖。

Example:

例：

// Java program to demonstrate the example of // Java ArrayList make Read-Only by using // unmodifiableCollection() method of Collections classimport java.util.*;public class ArrayListMakeReadOnly {public static void main(String[] args) {// ArrayList DeclarationCollection arr_list = new ArrayList();// By using add() method to add few elements in // ArrayListarr_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-OnlyCollection 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

輸出量

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

翻譯自: https://www.includehelp.com/java/make-arraylist-read-only-in-java.aspx

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