I want to update value of "status" and "amount" Json String
{  
     "installmentno":"1",
     "receiptid":"",
     "duedate":"12-10-2016",
     "paymentdate":"",
     "amount":"3000.00",
     "status":"unpaid"
}
I want to update value of "status" and "amount" Json String
{  
     "installmentno":"1",
     "receiptid":"",
     "duedate":"12-10-2016",
     "paymentdate":"",
     "amount":"3000.00",
     "status":"unpaid"
}
 
    
    The cleanest way is convert Json to object, change values, and convert again to String Json:
Other methods:
If exists only one occurence of value in Json String, and you know current value, use: String.replace("oldValue", "newValue");
Use 
String.replaceAll("regex", "newValue"); 
and regular expression
