Java Basics: Variable Naming Rules and Conventions

One of the important things to learn regarding java programming language is what is allowed and not allowed in choosing the name of a variable. Basically there are rules for choosing the name of a variable and there are conventions. In this post, we will be learning about the rules that govern variable naming in java language in addition to the conversions that is used by any java developer. We will include code examples to illustrate naming rules.

Naming Rules

1 - Variable name can start only with a letter, underscore (_) or dollar sign ($).

//This is allowed
int firstNum;

//This is allowed
int FirstNum;

//This is allowed
int _firstNum;


//This is allowed
int $firstNum;


//This is not allowed
int !firstNum;



2 - Variable name can contain numbers after the first letter.

//This is allowed
int burger1;


//This is not allowed
int 1burger;

//This is allowed
int burger2;


3 - Variable name cannot contain spaces or special characters.

//This is not allowed
int burger 1;

//This is not allowed
int burger-2;

//This is not allowed
int burger(3);


4 - Uppercase name differ from lower case.

//This one variable
int burger;


//This one is another one
int BURGER;

//Also this one is not same as above
int BURGer;


5 - Java keywords cannot be used for variable name (e.g. void).

//not allowed
int void;



6 - The length of the variable can be of any length.

Naming Conventions

Naming conventions are used by the developers to understand the meaning of a variable. For example, if you wrote a code and someone else reads that code, he will be able to understand your code easier if you use naming conventions. I my self follow the given conversions when I write Java code.

The following naming conventions are good to follow when you start writing your code:

• Do not use dollar sign or underscore in the name of your variables.
• Use meaningful names.
• Use uppercase letters for the constant variables(e.g. PI = 3.14).
• If the constant has two words, use underscore to separate words (e.g. MAX_SIZE = 4).

Java Basics: Type Casting

What do we mean by "Type Casting"?

Type casting is basically the process of changing or converting one variable from one data type to other different data types. For example, we may want to convert an integer variable data type to a long data type. For the primitive data types, The type casting can be performed only on the numbers. We can think of a char data type as a number since it is one of the Integral Data Types. We cannot perform casting on boolean.

What is an Integral Data Type?

An integral data type is a data type that represents a subset of the infinite integer set (such as byte, short, int, char, long in Java Language).

For the primitive data types, we have two types of conversion:

• Narrowing primitive conversion
• Widening primitive conversion

Before we continue with the meaning of each one, we have to know few things. Java data types are grouped into 3 groups, The Integral Types, Floating and the boolean. The integral group contains the types that does not have a decimal point. It includes the int, byte, short, long and the char. The floating group contains the types that has a decimal point. The floating group contains two data types, the double an the float. The boolean group contains only the boolean data type. Each data type has a specific size. The double is 64 bits, the long is 64 bits, the float is 32 bits, the int is 32 bits, the short is 16 bits, the char is 16 bits and the byte is 8 bits.

The next table shows the summary of data types sizes.

Group	Data Type	Size
Floating	double	64 bits
	float	32 bits
Integral	long	64 bits
	int	32 bits
	short and char	16 bits
	byte	8 bits

Widening Primitive Conversion

Sometimes called Automatic Type casting. It can happen when we try to cast a small size type to a larger size type. For example, we may want to convert from a short to an int. Also we can cast from Integral type to floating type in widening primitive conversion.

Group	Data Type	Size	-
Floating	double	64 bits
	float	32 bits
Integral	long	64 bits
	int	32 bits
	short and char	16 bits
	byte	8 bits

This type of casting does not require any special thing in order to be completed. The next code example shows how it can be done.



public class Main{
  public static void main(String [] arguments){

    //the original value
    byte myByte = 65;

    //changing from byte to short
    short byteAsShort = myByte;

    //changing from byte to integer
    int byteAsInt = myByte;

    //changing from byte to double
    double byteAsdouble = myByte;

    //from long to double. Notice the 'L'
    double longAsDouble = 77L;

    //from float to double. Notice the 'F'
    double floatAsDouble = 67F

    System.out.println("byte = "+myByte);
    System.out.println("byte as short = "+byteAsShort);
    System.out.println("byte as integer = "+byteAsInt);
    System.out.println("byte as double = "+byteAsdouble);
    System.out.println("byte as double = "+byteAsdouble);
    System.out.println("long as double = "+longAsDouble);
    System.out.println("float as double = "+floatAsDouble);
  }
}



One thing to notice about widening primitive conversion is when we try to cast a byte or a short to a char. In order to cast from byte to char, we have to till the compiler that we are changing from byte to char. Same thing apply when we are casting from short to char. The following code example shows how to do that.



public class Main{
  public static void main(String [] arguments){

    //the original value
    byte myByte = 65;
    //changing from byte to short
    short byteAsShort = myByte;
    //changing from byte to character. Notice the '(char)' thing that we have added
    char byteAsChar = (char)myByte;
    System.out.println("byte = "+myByte);
    System.out.println("byte as short = "+byteAsShort);
    System.out.println("byte as char = "+byteAsChar);
  }
}



Narrowing Primitive Conversion

Narrowing primitive conversion is the opposite of Widening primitive conversion. What we do is we convert a larger size data type to a smaller one. To complete this task, we have to tell the compiler explicitly about the conversion. We do that by doing the same thing when we wanted to convert from byte to char.

Group	Data Type	Size	-
Floating	double	64 bits
	float	32 bits
Integral	long	64 bits
	int	32 bits
	short and char	16 bits
	byte	8 bits

The following code example shows how it is done.



public class Main{
  public static void main(String [] arguments){

    //the original value 
    double myDouble = 65.3456;
    //changing from double to float 
    float doubleAsFloat = (float)myDouble;

    //changing from double to long
    long doubleAsLong = (long)myDouble;

    //changing from double to int 
    int doubleAsInt = (int)myDouble;
     
    //from double to short 
    short doubleAsShort = (short)myDouble;

    //from double to char
    char doubleAsChar = (char)myDouble;

    //from double to byte 
    byte doubleAsByte = (byte)myDouble;
    System.out.println("double = "+myDouble);
    System.out.println("double as float = "+doubleAsFloat);
    System.out.println("double as long = "+    doubleAsLong);
    System.out.println("double as int = "+doubleAsInt); 
    System.out.println("double as short = "+doubleAsShort);
    System.out.println("double as char = "+doubleAsChar);
    System.out.println("double as byte = "+doubleAsByte);

  }
}



What Happened to the Decimal Point when We cast from float or double to a type that has no Decimal Point? When we cast from floating type to integral type, the number will be always truncated (the numbers after the decimal point will be cut down).



public class Main{
  public static void main(String [] arguments){

    //the original values
    double firstDouble = 88.49;
    double secondDouble = 88.50;
    double thirdDouble = 600.90;
    double fourthDouble = 600.0001;

    //changing from floating to integral type
    int firstDoubleAsInt = (int)firstDouble;
    int secondDoubleAsInt = (int)secondDouble;
    int thirdDoubleAsInt = (int)thirdDouble;
    int fourthDoubleAsInt = (int)fourthDouble;

    System.out.println("first double = "+firstDouble);
    System.out.println("first double as int = "+firstDoubleAsInt);
    System.out.println("second double = "+secondDouble);
    System.out.println("second double as int = "+secondDoubleAsInt);
    System.out.println("third double = "+thirdDouble);
    System.out.println("third double as int = "+thirdDoubleAsInt);
    System.out.println("fourth double = "+fourthDouble);
    System.out.println("fourth double as int = "+fourthDoubleAsInt);
  }
}