A Tale of 4 Variables

transcript

intX intY char c

double d

Once upon a time…

There was a program

And in that program there were methods A click method

And the main method

public void click()

public static void main()

And in the methods…There were variables

And the variables were declared

Creating space in memory to hold information

int intX;

int intY; intX

public void click() {

But the variables were emptyThere was nobody home.

And different kinds of variables hold different kinds of information Are you happy?

That’s true or false boolean

What’s your middle initial? That’s a single letter char

How far away do you live? That’s a number, it could include a fraction or decimal double

And the assignment statementwas executed And it gave values to the variables

intX = 8; intY = 5;

Just be sure to declare the right kind of variable to hold the right kind of information

Which ones are correct types? int distance = 45.5;boolean happy = false;char initial = “Tom”;double distance = “far away”;char letterGrade = ‘A’;boolean b = “true”;

This is also called a floating point value, it has a decimal

point. An integer does

Of course, assignment is not the same as equals intX = intX + 3;

The algebra teacher said

The computer teacher said

No number can equal itself plus 3

= means

Always do the equation on the

right first, then assign the

result to the variable on the left

So… intX = intX + 3

Means…First take the value of intXAdd 3Store the result in intX

This is a literal value, it’s the same every time the program runs, intX is a variable, it can change

And the students were happy

Because they understood

And the students could assign values to variables They knew that after the assignment

statement intX = intY + intX * 2

intX =

So whenever you want to remember information in a program Or if you want to leave a fill-in-the-blank

space to be filled in later (like a Mad Lib) Use a variable to store the information

Rules for making up your own variable names: Must start with a letter Can use numbers, letters and underscores

(_) Cannot use a work that already has a

special meaning in Java like:mainvoidsystem

Which identifiers do NOT follow the rules for Java variables? length println happyCamper best friend ready?

good4u 2many tax_amount total! b45

A Tale of 4 Variables

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