coll_makero.html

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<TITLE>Making a Collection Read-Only
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  <h3>
    e348.  
    Making a Collection Read-Only</h3>

Making a collection read-only involves wrapping the collection in
another object whose mutation methods all throw
<code>UnsupportedOperationException</code>.


<pre>
    List stuff = Arrays.asList(new String[]{<font color="#0066ff"><i>"a"</i></font>, <font color="#0066ff"><i>"b"</i></font>});
    
    // Make a list read-only
    List list = new ArrayList(stuff);
    list = Collections.unmodifiableList(list);
    
    try {
        // Try modifying the list
        list.set(<font color="#0066ff"><i>0</i></font>, <font color="#0066ff"><i>"new value"</i></font>);
    } catch (UnsupportedOperationException e) {
        // Can't modify
    }
    
    // Make a set read-only
    Set set = new HashSet(stuff);
    set = Collections.unmodifiableSet(set);
    
    // Make a map read-only
    Map map = new HashMap();
    // Add key/value pairs ...
    map = Collections.unmodifiableMap(map);
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            &nbsp;Related Examples
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e342. <a class="eglink" href="coll_Queue.html?l=rel">
    Implementing a Queue
</a>
<br>

e343. <a class="eglink" href="coll_Stack.html?l=rel">
    Implementing a Stack
</a>
<br>

e344. <a class="eglink" href="coll_Cache.html?l=rel">
    Implementing a Least-Recently-Used (LRU) Cache
</a>
<br>

e345. <a class="eglink" href="coll_Iterate.html?l=rel">
    Listing the Elements of a Collection
</a>
<br>

e346. <a class="eglink" href="coll_StorePrimitive.html?l=rel">
    Storing Primitive Types in a Collection
</a>
<br>

e347. <a class="eglink" href="coll_CreateCopy.html?l=rel">
    Creating a Copy of a Collection
</a>
<br>


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        See also: 
<a class="eglink" href="/egs/java.util/pkg.html?l=rel#Arrays">
    Arrays
</a>&nbsp;&nbsp;

<a class="eglink" href="/egs/java.util/pkg.html?l=rel#Bits">
    Bits
</a>&nbsp;&nbsp;

<a class="eglink" href="/egs/java.util/pkg.html?l=rel#Dates">
    Dates
</a>&nbsp;&nbsp;

<a class="eglink" href="/egs/java.util/pkg.html?l=rel#Hash%20Tables">
    Hash Tables
</a>&nbsp;&nbsp;

<a class="eglink" href="/egs/java.util/pkg.html?l=rel#Lists">
    Lists
</a>&nbsp;&nbsp;

<a class="eglink" href="/egs/java.util/pkg.html?l=rel#Property%20Files">
    Property Files
</a>&nbsp;&nbsp;

<a class="eglink" href="/egs/java.util/pkg.html?l=rel#Sets">
    Sets
</a>&nbsp;&nbsp;

<a class="eglink" href="/egs/java.util/pkg.html?l=rel#Sorted%20Collections">
    Sorted Collections
</a>&nbsp;&nbsp;

<a class="eglink" href="/egs/java.util/pkg.html?l=rel#Time">
    Time
</a>&nbsp;&nbsp;

<a class="eglink" href="/egs/java.util/pkg.html?l=rel#Timers">
    Timers
</a>&nbsp;&nbsp;

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