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    <p>Basically <code>unModifiable</code> Collection is a view, So indirectly it could still be 'modified' from some other reference that is modifiable. Also as its just a <strong><em>readonly view</em></strong> of annother collection , When the source collection changes unModifiable Collection will always present with latest values.</p> <p>However <code>immutable</code> Collection can be treated as a <strong><em>readonly copy</em></strong> of another collection and can not be modified. In this case when the source collection changes , immutable Collection do not reflect the changes</p> <p>Here is a testcase to visualise this difference. </p> <pre><code>@Test public void testList() { List&lt;String&gt; modifiableList = new ArrayList&lt;String&gt;(); modifiableList.add("a"); System.out.println("modifiableList:"+modifiableList); System.out.println("--"); //unModifiableList assertEquals(1, modifiableList.size()); List&lt;String&gt; unModifiableList=Collections.unmodifiableList( modifiableList); modifiableList.add("b"); boolean exceptionThrown=false; try { unModifiableList.add("b"); fail("add supported for unModifiableList!!"); } catch (UnsupportedOperationException e) { exceptionThrown=true; System.out.println("unModifiableList.add() not supported"); } assertTrue(exceptionThrown); System.out.println("modifiableList:"+modifiableList); System.out.println("unModifiableList:"+unModifiableList); assertEquals(2, modifiableList.size()); assertEquals(2, unModifiableList.size()); System.out.println("--"); //immutableList List&lt;String&gt; immutableList=Collections.unmodifiableList( new ArrayList&lt;String&gt;(modifiableList)); modifiableList.add("c"); exceptionThrown=false; try { immutableList.add("c"); fail("add supported for immutableList!!"); } catch (UnsupportedOperationException e) { exceptionThrown=true; System.out.println("immutableList.add() not supported"); } assertTrue(exceptionThrown); System.out.println("modifiableList:"+modifiableList); System.out.println("unModifiableList:"+unModifiableList); System.out.println("immutableList:"+immutableList); System.out.println("--"); assertEquals(3, modifiableList.size()); assertEquals(3, unModifiableList.size()); assertEquals(2, immutableList.size()); } </code></pre> <p><strong>Output</strong></p> <pre><code>modifiableList:[a] -- unModifiableList.add() not supported modifiableList:[a, b] unModifiableList:[a, b] -- immutableList.add() not supported modifiableList:[a, b, c] unModifiableList:[a, b, c] immutableList:[a, b] -- </code></pre>
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    1. POImmutable vs Unmodifiable collection
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    1. USPrashant Bhate
    1. USPrashant Bhate
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    1. COI am not able to see any difference, Can you please point out how Immutable is different? I can see both Immutable and unmodifiable are throwing error and add is not supported. Am I missing something here?
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    2. CO@AKS Please see output of last three list entries after addition of 'c' to the list while both size of `modifiableList` and `unModifiableList` has increased `immutableList` size has not changed
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    3. COOh! got it! :).. So here you modified unmodifableList using the changes in modifiableList, but ImmutableList can not be modifed. But same way you can modify ImmutableList also, I think here client will get access to ImmutableList reference only, reference to modifiableList, using which ImmutableList is created, will not be exposed to client. right?
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