A question about string.trim()

Question

I got a fragment of code as follows:
String s = "abcd ";
boolean a = (s.trim()=="abcd");
boolean b = (s =="abcd ");
Why a is false, b is true?

Answer 1

The reason why the below code has true assigned to be is quite easy to explain:
String s = "abcd";
String y = "abcd";
boolean b = (s == y);
...The String class has a "Pool" of strings. When you use String literals; the compiler automatically checks if it is in the String pool already and if it exists; a reference to that String is returned; if not a new entry in the pool is added and then you get a reference to that. This is only true for Stirng literals and String created using the intern() method.
If you compile this code you will see that the strings are not equal:
public static void main(String args[])
  String s = "abcd";
  String y = args[0];
  boolean b = (s == y);
  System.out.println(b);
}This is because the "abcd" is in the String pool when your program starts; but because the value "abcd" passed in (is not created in the pool automaticlaly). Therefor they are two different String objects.
This code block shows that you can add Strings to the pool. The intern() method checks to see if the String is in the pool already and if it is it will return you a reference to it; if not it will create one and then return it.
public static void main(String args[])
  String s = "abcd ";
  String y = args[0].intern();
  boolean b = (s == y);
  System.out.println(b);
}- Chris