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    <p>Gson has some limitations regarding collections because of Java's type erasure. You can read more about it <a href="http://sites.google.com/site/gson/gson-user-guide#TOC-Collections-Examples" rel="noreferrer">here</a>.</p> <p>From your question I see you're using both <code>ArrayList</code> and <code>LinkedList</code>. Are you sure you didn't mean to use just <code>List</code>, the interface?</p> <p>This code works:</p> <pre><code>List&lt;String&gt; listOfStrings = new ArrayList&lt;String&gt;(); listOfStrings.add("one"); listOfStrings.add("two"); Gson gson = new Gson(); String json = gson.toJson(listOfStrings); System.out.println(json); Type type = new TypeToken&lt;Collection&lt;String&gt;&gt;(){}.getType(); List&lt;String&gt; fromJson = gson.fromJson(json, type); System.out.println(fromJson); </code></pre> <p><strong>Update</strong>: I changed your class to this, so I don't have to mess around with other classes:</p> <pre><code>class IndicesAndWeightsParams { public List&lt;Integer&gt; indicesParams; public List&lt;String&gt; weightsParams; public IndicesAndWeightsParams() { indicesParams = new ArrayList&lt;Integer&gt;(); weightsParams = new ArrayList&lt;String&gt;(); } public IndicesAndWeightsParams(ArrayList&lt;Integer&gt; indicesParams, ArrayList&lt;String&gt; weightsParams) { this.indicesParams = indicesParams; this.weightsParams = weightsParams; } } </code></pre> <p>And using this code, everything works for me:</p> <pre><code>ArrayList&lt;Integer&gt; indices = new ArrayList&lt;Integer&gt;(); ArrayList&lt;String&gt; weights = new ArrayList&lt;String&gt;(); indices.add(2); indices.add(5); weights.add("fifty"); weights.add("twenty"); IndicesAndWeightsParams iaw = new IndicesAndWeightsParams(indices, weights); Gson gson = new Gson(); String string = gson.toJson(iaw); System.out.println(string); IndicesAndWeightsParams fromJson = gson.fromJson(string, IndicesAndWeightsParams.class); System.out.println(fromJson.indicesParams); System.out.println(fromJson.weightsParams); </code></pre>
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    1. COHi, Thanks for the help. My object is not a generic but rather contains two arraylists. how should i use the type ?<br>Type type = new TypeToken<myObj>(){}.getTrype doesnt work :-(
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    2. CObtw : two arraylist with two differnet objects. I just changed it to List <obj1> and List <obj2>
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    3. CO@user450602: edit your post and add code of your object and your arraylists. I don't want to guess anything.
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