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I have my program that displays a message and in that same message the user must enter a code. I’m trying to validate whether he typed something or not, so I use the code:
AlertDialog.Builder alert = new AlertDialog.Builder(context);
    alert.setTitle("Código final"); //Set Alert dialog title here
    alert.setMessage("Insira o código fornecido pela Nobre de la Torre:"); //Message here
    // Set an EditText view to get user input 
    final EditText input = new EditText(context);
    alert.setView(input);
    alert.setPositiveButton("OK", new DialogInterface.OnClickListener() {
    public void onClick(DialogInterface dialog, int whichButton) {
     //Ações do botão da mensagem
     String srt = String.valueOf(input.getEditableText());
     if(srt!=""){ //ESSE É O IF QUE ESTÁ COM ERRO
     Toast.makeText(context,srt,Toast.LENGTH_LONG).show();  
     }
     else
     {
     Toast.makeText(context,"Campo vazio!",Toast.LENGTH_LONG).show();  
     }  
      String hexNumber = srt;
      int decimal = Integer.parseInt(hexNumber, 16);
      System.out.println("Hex value is " + decimal); 
                 [COntinua...]
Even with the variable String srt being "" he sees as different from "" and execute the code below it
String srt = String.valueOf(input.getEditableText());
if(srt!=""){ 
    Toast.makeText(context,srt,Toast.LENGTH_LONG).show();
}
Since he should execute the else : 
else {
    Toast.makeText(context,"Campo vazio!",Toast.LENGTH_LONG).show();}
http://answall.com/questions/3905/como-comparar-strings-em-java
– Piovezan