Strings Redefined

Primitive v. Class Data Types

Primitive

  • Holds only one piece of data at a time
  • Example: int and double

Class

  • Holds more than one piece of data at a time
  • Can hold data of different types
  • Has built in methods

How are variables stored in memory?

Primitive Types

  • The variable holds the actual value.

    int num1 = 17;

Class Types

  • The variable holds the memory location of the actual data - refers to it

    String word1 = "Hello";

What if there is no reference?

String word;
  • What does word hold?
  • null - special value that means “no reference.”

Garbage Collection

String alpha = "The final frontier";
alpha = null;
  • What happens to “The final frontier”?
  • It is Garbage Collected.
  • Java goes through and “cleans up” any unmatched values in memory.

So why can’t I use ==?

String a = "Howdy";
String b = "Howdy";
  • The == tests the value stored directly in a and b.
  • These are two different memory locations
  • Prove the point:
if (a.equals(b));
if (a.substring(int));
if (a.substring(int, int));