Java lessons learned - Naming Convention, Variables,Data Types, Arrays

Data Types – 2 types

Naming conventions for JAVA units

1.Primitive Variables

Ex : int x = 8 ;

Type Bit-Depth Value-Range Default value

boolean JVM specific true,false false

char 16 bits 0 to 65535

byte 8 bits -128 to 127

short 16 bits -32768 to 32767

int 32bits -2147483648 to 2147483647

long 64 bits -huge to huge

float 32 bits varies

double 64 bits varies

2.Reference Varibales

Ex : Dog myDog = new Dog();

The value of the variable is bits representing a way to get to a specific object

(.) Dot operatore is used to refer the value in reference variable.

It's default value is null when not referening any object.

Arrays - it is always an object.

ex: nums = new int[7];

Once you declared an array, you can't put anything in it except things that are of the declared array type.

However you can put a byte into an int array. it is implicit widening.

Class - is a blueprint for an object.
Description for JVM to make object is nothing but a class.
Class consists instances (instance variables) and methods.
Mark instance variables private
Mark getters and setters public(get and set methods)
Instance variables always gets default value.
Local variables(variables in methods) do NOT get a default value.Compiler reports error for this.
Use == to compare two primitives or two references ex : int a = 4; int b = 4; if (a == b) print x;
USe the equals() method to see if two different objects are equal(such as two different String objects).
Java uses pass by value - " pass by value is passing by copy".

Wednesday, October 08, 2008 // Labels: Java // 1 comments //

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