title: Json String - How to add variables in the string
body: <p>I have a Json string like below</p>
  
  <pre><code> String jsonRequestString = "{\"access_code\" : \"9bPbN3\" , "
                            + "\"merchant_reference\" : \"123\", \"language\" : \"en\",\"id\" : \"149018273\","
                            + "\"merchant_identifier\" : \"gKc\", \"signature\" : \"570fd712af47995468550bec2655d9e23cdb451d\", "
                            + "\"command\" : \"VOID\"}";
  </code></pre>
  
  <p>I have a String variable as </p>
  
  <pre><code>String code = "9bPbN3";
  </code></pre>
  
  <p>Question, how do I plugin the above string  instead of hardcoding it at the below place. i.e. instead of 9bPbN3, I want to use the variable code there.</p>
  
  <pre><code>   String jsonRequestString = "{\"access_code\" : \"9bPbN3\" , "
  </code></pre>
  
  <p>Many Thanks in advance. </p>