Know Your Variables — Chapter 3

There are 2 types of variabels.

1. Primitive — Holds fundamental values including integers, booleans, and floating point numbers.
2. Object References — Holds references to objects.

Note:

Using of ‘f’ at the end of the value is needed for a variable to be explicitly declared as a float, since Java assumes every decimal value to be a double by default.

float f=32.5f;

Naming conventions for a class,method, variable

1. It must start with a letter or an underscore (_), or dollar algn ($). You can’t start a name with a number.
2. After the first character, you can use numbers as well.
3. It shouldn’t be one of Java’s reserved words.

Object References

• There is no such thing as an object variable. (Only an object reference variable)
• It holds something like a pointer.
• Objects live on the garbage collectible heap.
• Performing arithmetic operations in Java(increments etc.) on a reference variable, is not possible unlike C.
• Unless an object reference is final, one Dog object could refer to another Dog object later.
• Objects can also be assigned as null.

A bit about being null

• null is a value.
• If there is only one reference to a particular object, then once its set to null (deprogrammed), the object is lost.
• Unlike primitives, every lost object goes into garbage collection(GC).

Arrays

• An array could also be considered an object reference as it holds the references to the primitives/object references inside of it.
• An array itself is never a primitive (regardless of what the array holds), it is always an object.
• Accessing an unassigned index on an array of objects will give null.
• Accessing a value within an unassigned index on an array of objects will give a runtime error.

Vocabulary

Implicit widening — Although you can’t put a bigger size variable’s value inside a smaller, you can put do other way around. This is done using implicit widening.