References, Operators, Equality, and Strings

• Assignment and argument passing for non-primitives is done using references.

• Internally, a reference is like a pointer, except that the programmer does not have to dereference it or deal with pointer arithmetic because Java does this automatically.
  
  
• Two important points to remember related to references:
  
  
  1. If you want two objects to actually be separate objects that have the same values, use new. If you do not, changing a value in one object will also change the value in the other since they will point to the same object in memory.
     
     
  2. Non-primitive arguments are pass by reference, so if an argument is changed in a method, the object's value is really changed, even after the method returns.


• Java does not support operator overloading, you must use methods instead.

• Equality (= = and != ) is an exception, but they do not work the way you might expect!

• When used with class instances, equality checks if the two objects are the same reference (point to the same memory) and not if the two objects have the same value.

• For instance, the String class uses the equals() method to compare the values of two strings.

• Be careful with string literals. Java optimizes strings by storing the value of each string literal once and giving you pointers to this value wherever the string is used.

• Remember to use new when you want to have distinct objects:

String s1 = new String("Cathy");
String s2;

s2 = s1;        // same spot in memory

if (s1 == s2)       // true
    ...

s2 = new String(s1);    // each have their own memory

if (s1 == s2)       // false, and probably WRONG!
    ...

if (s1.equals(s2))  // true, and probably what you really want!
    ...