what is wrong with this boolean ?

Question

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Java

  String path = "C:\\Users\\User_2\\Pictures";
   
  String files;
  File folder = new File(path);
  
  
  File[] listOfFiles = folder.listFiles(); 
 
  int dot;
  
  for (int i = 0; i < listOfFiles.length; i++) 
  {
   
   if (listOfFiles[i].isFile()){
   files = listOfFiles[i].getName();
   System.out.println(files);
      dot = files.lastIndexOf(".");
   System.out.println(files.substring( dot + 1));
// why this allows equals false......
   System.out.println(files.substring(dot + 1) == "jpg");
  }
  }

Posted 24-Aug-12 11:42am

ahmed tb

Updated 24-Aug-12 12:24pm

v2

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Comments

pasztorpisti 24-Aug-12 18:27pm

And where is the boolean?

enhzflep 24-Aug-12 18:58pm

Presumably here?
files.substring(dot + 1) == "jpg"

pasztorpisti 24-Aug-12 19:03pm

My bad, thanks! Found it! :-)

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pasztorpisti · Accepted Answer · 2012-08-24T13:02:00

This expression compares the references that "point" to two different string objects. You compare the references ("the pointers") and the the string objects. This gives you false if you compare th references to two distinct string objects even if their value is the same.

Java

files.substring(dot + 1) == "jpg"

Use ths code if you want to compare the contents of the objects instead of the references:

Java

"jpg".equals(files.substring(dot + 1))

I call the method of the "jpg" string object because that is a constant and isn't null for sure and equals() handles well when its parameter is null.

what is wrong with this boolean ?

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