JAVA variable type and data type

In the JAVA language if you want to use variables, then you have the necessary declaration

JAVA data is divided into two types, one is the basic type, the other is a reference type.

Basic types:
byte (bits 1 byte. 8)
Sort (bit 2 of byte 16)
int (32 Bit 4 bytes)
Long (64 bits 8 bytes)
a float (32 Bit 4 bytes)
Double ( 64 8 bytes)
Boolean (32 4 bytes)
char (2 16 bytes)
mentioned above are generally 32-bit and 64-bit for the operating system
if it is 16-bit operating system bit and byte halved

Reference types: JAVA objects

JAVA variable types

• Instance variables
• Local variables
• Class variables

Local variables

• Statement method, constructor, or block of statements in
• Local variables are created when executed method, construction method statement block, once finished, will immediately be destroyed out
• Access modifier can not modify local variables
• Local variables only, method of construction statement block, the method can be seen
• When local variables created on the stack of open space
• Local variables without initial value, only given an initial value at the time of creation, before you can use

public class Test{ 
   public void pupAge(){
      int age = 0;
      age = age + 7;
      System.out.println("Puppy age is : " + age);
   }
   
   public static void main(String args[]){
      Test test = new Test();
      test.pupAge();
   }
}

Instance variables (member variables)

• In the class declaration, but in the method, constructor, an outer block of statements
• When a variable is instantiated, the value of each variable is determined to follow
• In the instance variables created when the object is created, destroyed when the object is destroyed
• Instance variable is referenced at least a method, constructor, or block of statements, so that the external variable information can be acquired by these methods.
• Instance variables can be declared before use or after use
• Access modifier can be modified instance variables
• Instance variables in the general method, constructor, visible statement block, half of the private instance variables set, can be made by accessing the instance variables of the class modifiers visible
• Examples of boolean variables have a default value defaults to false, int default is 0, the default value instance variable is null
• Declare instance variables can be specified by the user other methods;
  instance variables can be directly accessed by the variable name. However, static methods and other classes, you should use the fully qualified name: