More on Data Types

The 4 common primitive data types were covered previously; this node will look at all the different data types in more depth.

In Java everything is an Object except the primitive types which represent actual data in memory. Java uses primitive types to keep things optimized for the computer, though it makes it a bit more confusing for the programmer.

No Object is created when assigning primitive types, so you can just assign a variable a literal value without any new keyword. For example:

int num = 5;
char ch = 'c';

Each type in Java takes up a certain amount of memory and can therefore hold a certain range of values. The size in measured in bits, i.e. a single 1 or 0. The range of an integer data type is simply 2^bits. For example, an 8-bit number will be able to hold 256 values.

integer types

There are 4 integer data types in Java. byte and short are the 2 uncommon ones, which you may never need:

• byte - This can store integers from -127 to 127. You may have guessed that they take up one byte of memory, or 8 bits. It is sometimes used when dealing with raw data or in special low-memory circumstances.
• short - This is a 16-bit type that can store integers from –32,768 to 32,767. It is almost never used.

The next two integer types are more common:

• int - This is a 32-bit type which can store numbers from –2,147,483,648 to 2,147,483,647. int is used for almost all integers in Java, even small ones. For example, its used as a counter in loops and to track locations in arrays.
  It is not necessary (or even helpful) to use a byte or short instead of an int for small integer values. When you write an integer literal like 3 or 1234 in Java, it is assumed to be of type int.
• long - The int can go from about -2 Billion to +2 Billion, but sometimes you need to deal with longer numbers. This is where long is useful. It is a 64-bit type which can store numbers from - 2⁶³ to 2⁶³ (which is a 9 followed by 18 digits.)
  To mark a number as a long you put a L after it. For example:

  long num1 = 123456789000L;
  long num2 = 12L

floating-point types

The above types can only deal with integers, so any decimal numbers that come up will be rounded down to integers. For example System.out.println(5/2); will print 2 instead of 2.5.

This is because 5 and 2 are assumed to be integers, and during division any decimal value is lost. To keep decimal values, you need to use floating-point types. There are 2 types for holding "decimal", or real numbers, like 2.25 and 0.003:

• float - this is a 32-bit type for storing real numbers which can be useful for simple values. It will become imprecise when used in operations with very large or very small values. To create a float value, you need to add an f after the number. For example, float f = 1.23f;
• double - this is a 64-bit type for storing real numbers, which should generally be used. A number with a decimal value (like 1.23) is assumed to be a double in Java.
  

characters

The char type is is used in Java for storing a single character of text. A char is a single character enclosed in single quotes. For example:

char c = 'x';
char d = '5';

A char can also store many values that do not appear on the keyboard. These are specified using special sequences that are 'escaped' with the \. The most common one is the newline character: '\n', which is used to create a newline (usually in Strings). To store words of text, you use the String type, which uses characters internally for storage.

chars are really numbers
The char in Java is a 16-bit type for representing any unicode character. The char is stored as an integer in the computer with a range from 0 to 65,535. Since char is stored as an integer, it can be treated as one too. For example, you can add to a char:

char c1 = 'a';
char c2 = 'a' + 1;
System.out.println("c2 is " + c2);

This will print:

c2 is b

This is because b is represented by an integer 1 more than a (specifically 98 and 97). In fact, all the alphanumeric characters are represented by integers in order, so you could always add 1 to a letter to get the next letter.

Since characters can be integers, you need to watch out for the following error:

System.out.println(c1 + c2);

You might expect this to print ab like it would for Strings a and b. However, since chars are integers, Java will add their values together and print 195 instead. + is used to concatenate Strings, but when dealing with numbers it will add them.