Lesson 4

Input

JAVA Input

• JAVA input is not straightforward and is different depending on the JAVA environment that you are using.

• The reason it is not straightforward, is that JAVA is a complete object-oriented package, whereas every method must be an object.

• In other words, there is not a simple built-in command that is universal amongst compilers (i.e. cin for C++, input for Basic)

Example Program with Inputimport TerminalIO.KeyboardReader;

public class Convert{

public static void main(String [] args){

KeyboardReader reader = new KeyboardReader();double fahrenheit;double celsius;

System.out.print(“Enter degrees Fahrenheit: “);fahrenheit = reader.readDouble();celsius = (fahrenheit – 32.0) * 5.0/9.0;System.out.print(“The equivalent in Celsius is “);System.out.println(celsius);reader.pause();

}}

Example Program Explanation

• The import statement incorporates a file from your computer into your program.

• The KeyboardReader class which is imported gives us the functionality to get input from the keyboard.

• Without this statement you will not be able to input information.

Import TerminalIO.KeyboardReader;

Example Program Explanation

• This statement instantiates or creates a KeyboardReader object.

• It’s name “reader” is an arbitrary name and can be called anything that you want.

• NOTE: An object is always an instance of a class and must be created, or instantiated before being used.– i.e. SomeClass someobject = new

SomeClass()

KeyboardReader reader = new KeyboardReader();

Example Program Explanation

• This defines two numeric variables that will be used to hold the input and calculate the result for output.

• double means that the numbers are floating point numbers (i.e. they can contain decimals)

double fahrenheit;double celsius;

Example Program Explanation

• This statement creates a prompt in the output window.

• Prompt – A print or println statement that tells the user at the console window that something is to be entered.

• You must always prompt the user for the input.

System.out.print(“Enter degrees Fahrenheit: “);

Example Program Explanation

• This statement gets the value that is entered from the keyboard into the variable “fahrenheit”

• The reader object waits for a number to be input and the enter key to be pressed.

• Once that is done, it returns that value to “fahrenheit”.

fahrenheit = reader.readDouble();

•  char readChar()        

•  double readDouble()

•  int readInt()  

• String readLine()           

Example Program Explanation

• This statement contains the actual calculation for converting fahrenheit to celsius.

• This is called an assignment statement.• In an assignment statement, you cannot

have any calculations on the left hand side of the =. You can only have variables.

• On the right hand side, you can have variables and math operators.

celsius = (fahrenheit – 32.0) * 5.0/9.0;

Example Program Explanation

• These statements place the output in the console window.

• The first statement labels the data that is being output.

• The second statement prints out the value that is contained in the memory location for celsius.

System.out.print(“The equivalent in Celsius is “);System.out.println(celsius);