A Tale of 4 Variables

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A Tale of 4 Variables intX intY char c double d

description

intX. intY. char c. double d. A Tale of 4 Variables. 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(). intX. intY. And in the methods… There were variables. - PowerPoint PPT Presentation

Transcript of A Tale of 4 Variables

Page 1: A Tale of 4 Variables

A Tale of 4 Variables

intX intY char c

double d

Page 2: A Tale of 4 Variables

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()

Page 3: A Tale of 4 Variables

And in the methods…There were variables

And the variables were declared

Creating space in memory to hold information

int intX;

int intY; intX

intY

public void click() {

But the variables were emptyThere was nobody home.

Page 4: A Tale of 4 Variables

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

Page 5: A Tale of 4 Variables

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

intX = 8; intY = 5;

intY

intX

8

5

Page 6: A Tale of 4 Variables

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

not.

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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

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So… intX = intX + 3

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

intX

8

8 + 3

=11

intX

11

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

Page 9: A Tale of 4 Variables

And the students were happy

Because they understood

Page 10: A Tale of 4 Variables

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

statement intX = intY + intX * 2

intX =

intX

11

intY

5

intX

27

Page 11: A Tale of 4 Variables

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

intY

5

Page 12: A Tale of 4 Variables

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

Page 13: A Tale of 4 Variables

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

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