The following table contains a list of the basic arithmetic operators.

Even within this range of types of data one needs to consider issues about the precision of the representation within the computer.  Things that are true or false require nowhere near as much memory to store as the numbers associated with space travel.

But this motivates the classification of data into what are usually called data types.

In Java there are some standard data types listed in the following tables. we also present some information about the ranges of representation and the amount of memory that is used.

First we list what are called the primitive data types.  Then we will present some derived data types that are worked with in their own classes.

Meaning

A Program for Expressions.  The following Java applet just requests that the user input two different numbers.  It then parses them as floats and casts them to integers.  Then it computes their quotient and modulus and displays the result.  You need to call the file ExpressionsOperators.java.

public void init()
{

String firstUserEntry, secondUserEntry;
int a, b, intQuotient, intModulus;
float floatA = 0;
float floatB = 1;
float floatQuotient, floatModulus;
JTextArea outputArea = new JTextArea();


// Prompt user for input
firstUserEntry = JOptionPane.showInputDialog("Please enter a number:");

// convert these string values to integers
try
{

floatA = Float.parseFloat(firstUserEntry);

}

catch (NumberFormatException nfeFloat)
{

JOptionPane.showMessageDialog( null, "The first entry needs to be a number",
"Not a Float", JOptionPane.INFORMATION_MESSAGE);
System.exit(0);

}


// Prompt user for second input
secondUserEntry = JOptionPane.showInputDialog("Please enter another number:");

try
{

floatB = Float.parseFloat(secondUserEntry);

}

catch (NumberFormatException nfeFloat)
{

JOptionPane.showMessageDialog( null, "The second entry needs to be a number",
"Not a Float", JOptionPane.INFORMATION_MESSAGE);
System.exit(0);

}

// casting the floats to integers
a = (int) floatA;
b = (int) floatB;

// computing the integer solution
intQuotient = a/b;
intModulus = a % b;

// computing the float solutions
floatQuotient = floatA/floatB;
floatModulus = floatA % floatB;


// displaying the solution
outputArea.setText("Data Type\ta\tb\ta/b\ta%b\n\n");

// displaying the integer solution
outputArea.append("Integer\t" + a+ "\t" + b + "\t" + intQuotient + "\t" + intModulus + "\n\n");

// displaying the floating point solution

outputArea.append("Float\t" + floatA+ "\t" + floatB + "\t" + floatQuotient + "\t" + floatModulus);

// displaying the textarea within an MessageDialog
JOptionPane.showMessageDialog( null, outputArea, "Solutions", JOptionPane.INFORMATION_MESSAGE);

} // end method init

} // end class ExpressionsOperator

• As usual the first section of code
  • imports the classes from external packages.  In this instance they all come from swing.
    • JOptionPane
    • JTextArea
    • JApplet
  • declares the overall class
  • declares the init( ) method that automatically executes in applets
  • declares and initializes variables
• the next section of code attempts to get the first number from the user
  • it contains the effort to parse it into a float within a try block
  • the catch block is set up to
    • trap for non-numeric inputs
    • give the user a message about the error
    • stably exit the program
• the next section of code attempts to get the second number from the user
  • it contains the effort to parse it into a float within a try block
  • the catch block is set up to
    • trap for non-numeric inputs
    • give the user a message about the error
    • stably exit the program
• the next section of code does the manipulation of the numbers
  • the floats are cast to integers for integer arithmetic
  • the integer quotient and modulus are computed
  • the float quotient and modulus are computed
• the output is put to the JTextArea
  • first a header row of text is set using tab and newline control characters
  • then the user's inputs cast to integers and the quotient and modulus are appended to the JTextArea
  • then the user's inputs used as floats and the quotient and modulus are appended to the JTextArea
• then this JTextArea is displayed within a JOptionPane showMessageDialog box.

You will also need to create the following ExpressionsOperators.html.

Now we will describe some other operators and operations that can be used to develop mathematical expressions.  We will make use of these in future web pages.

Assignments and Increments/Decrements.  You may have already encountered how an equal sign = is really an assignment operator in computing rather than an equal sign.  Thus statements like

x = 23.4 * ( x + 11.2 )

actually make sense.  Whatever,  x currently is you should add 11.2 to it and then multiply this sum by 23.4 to get the "new value" of x.

In Java, there are several other ways that certain fairly standard assignment operations can be performed.  The following table contains four of them.

It is also possible to increment and decrement a variable by one in a shorthand notation as shown in the  following table.

Comparisons.  Everyone that has reached college has seen things like > and < in order to make comparisons.  It is not very much different in Java.  The following  table contains the basic comparison operators for Java.

Meaning

The operators are in the following table.  We will give a few examples after the table.

( height > 60 ) && ( height < 70 )

If you don't care if they are exactly at the limits then the relevant expression would be

( height >=  60 ) && ( height <=  70 )

Or maybe you don't care what color their hair is.  This might be developed as the following.

( hairColor == "Blonde")  | |  ( hairColor == "Brown")  | |  ( hairColor == "Black")  | |  ( hairColor == "Red")

Well, we could go on and on with this.  But the next few webpages will focus on code that makes use of mathematical expressions and comparisons in order to make decisions.