Java Data Types in AP Computer Science A

What are Data Types?

Data types are the building blocks of any programming language. They are the fundamental units of storage that are used to store information in a program. Data types are used to define variables and methods in a program. They also define the operations that can be performed on the variables and methods.

Primitive Data Types

Primitive data types are the most basic data types in Java. They are the building blocks of all other data types. There are eight primitive data types in Java: byte, short, int, long, float, double, char, and boolean. The following table shows the size and range of each primitive data type.

Char and String

• char - A single character (e.g. 'a', 'b', 'c ', 'd', 'e', 'f', 'g', 'h', 'i', 'j')
• String - A sequence of characters (e.g. "Hello World!")

Numeric

• byte - A whole number between -128 and 127
• short - A whole number between -32,768 and 32,767
• int - A whole number between -2,147,483,648 and 2,147,483,647
• long - A whole number between -9,223,372,036,854,775,808 and 9,223,372,036,854,775,807

Floating Point

• double - A decimal number (e.g. 1.0, 2.0, 3.0, 4.0, 5.0, 6.0)
• float - A decimal number between 1.4E-45 and 3.4028235E38

Boolean

• boolean - A value that is either true of false

Declaring Variables

Variables are used to store data in a program. They are declared using the following syntax:

<type> <name>;
String word;

Assignment

Assignment is the process of assigning a value to a variable. The following table shows the syntax for assignment.

<type> <name> = <value>;
char letter = 'a';
String word = "Hello World!";
byte number = 1234;
short number = 22342;
int number = 2,147,483,645;
long number = 223,372,036,854,775,808;
double number = 5.0;
float number = 6.0;
boolean value = true;

Reference Data Types

Reference data types are data types that are not primitive. They are used to store objects. There are two types of reference data types: class and interface. The following table shows the size and range of each reference data type.

• class - A reference to an object of a class
• interface - A reference to an object of an interface

Specialized Data Types

Specialized data types are data types that are not primitive or reference. They are used to store objects. There are two types of specialized data types: array and enum. The following table shows the size and range of each specialized data type.

• array - A collection of objects of the same type

int[] numbers = {1, 2, 3, 4, 5};

• enum - A collection of objects of the same type. The objects are called enumerators.

enum Color {
  RED,
  GREEN,
  BLUE
}

Common Errors

Type Mismatch

Type mismatch occurs when a variable is assigned a value of a different type than the variable's type. For example, the following code will result in a type mismatch error because the variable number is of type int and the value 5.0 is of type double.

int number = 5.0;

Type Conversion

Type conversion is the process of converting a value of one type to a value of another type. There are two types of type conversion: implicit and explicit. Implicit type conversion is the process of converting a value of one type to a value of another type without the programmer's knowledge. Explicit type conversion is the process of converting a value of one type to a value of another type with the programmer's knowledge.

Implicit Type Conversion

Implicit type conversion is the process of converting a value of one type to a value of another type without the programmer's knowledge. For example, the following code will result in an implicit type conversion error because the variable number is of type int and the value 5.0 is of type double.

int number = 5.0;

Explicit Type Conversion

Explicit type conversion is the process of converting a value of one type to a value of another type with the programmer's knowledge. For example, the following code will result in an explicit type conversion error because the variable number is of type int and the value 5.0 is of type double.

int number = 5.0;

Summary

In this unit, you learned about the following data types:

• Primitive Data Types
• Reference Data Types
• Specialized Data Types

References

• Primitive Data Types

AP CSA Homework Assignment

Assignment

Instructions

Create a simple Java program that uses each of the primitive data types in a program. Use each of the reference data types in a program. Use each of the specialized data types in a program. Use each of the operations on data types in a program.

• Create a new Java project called DataTypes.
• Build a program of your choice.
• Use each of the primitive data types in a program.
• Use each of the reference data types in a program.
• Use each of the specialized data types in a program.
• Use each of the operations on data types in a program.

Some examples for projects:

• Build a simple calculator.
• Build a simple mortgage calculator.
• Build a simple BMI calculator.
• Build a simple GPA calculator.
• Build a simple tip calculator.
• Build a simple grade calculator.
• Build a simple retirement calculator.
• Build a simple savings calculator.
• Build a simple loan calculator.
• Build a simple car loan calculator.
• Build a simple compound interest calculator.