copyright © texas education agency, 20131 computer programming your first java program:...

12
Copyright © Texas Education Agency, 2013 1 Computer Programming Your First Java Program: HelloWorld.java

Upload: johnathan-sherman

Post on 17-Dec-2015

214 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Copyright © Texas Education Agency, 20131 Computer Programming Your First Java Program: HelloWorld.java

Copyright © Texas Education Agency, 2013 1

Computer Programming

Your First Java Program: HelloWorld.java

Page 2: Copyright © Texas Education Agency, 20131 Computer Programming Your First Java Program: HelloWorld.java

HelloWorld.java

1. // Name: your name here

2. // Date: today’s date here

3. // Program: HelloWorld.java

4. public class HelloWorld

5. {

6. public static void main (String[] args)

7. {

8. System.out.println ("Hello World!");

9. }

10. }

© UNT in partnership with TEA IT: Beginning Computer Programming- First Java Program 2

Page 3: Copyright © Texas Education Agency, 20131 Computer Programming Your First Java Program: HelloWorld.java

Comments

1. // Name: your name here

2. // Date: today’s date here

3. // Program: Hello World

Lines 1-3 are comments.

Comments begin with //

Comments are ignored by the compiler

Used to give information to the reader

Copyright © Texas Education Agency, 2013 IT: Beginning Computer Programming- First Java Program 3

Page 4: Copyright © Texas Education Agency, 20131 Computer Programming Your First Java Program: HelloWorld.java

Program Declaration

4. public class HelloWorld

Line 4 is the program declaration.

“public” is a key word indicating that the class file is usable by the public.

“class” indicates that the file is a program. Classes are the building blocks of Java.

“HelloWorld” is the name of the file. Java is case-sensitive. The file must be saved as “HelloWorld.java”.

Copyright © Texas Education Agency, 2013 IT: Beginning Computer Programming- First Java Program 4

Page 5: Copyright © Texas Education Agency, 20131 Computer Programming Your First Java Program: HelloWorld.java

Braces

5. {

Line 5 begins the program with an opening curly brace({)

Braces enclose statements that make up a programming block.

Each opening brace must have a matching closing brace.

Copyright © Texas Education Agency, 2013 IT: Beginning Computer Programming- First Java Program 5

Page 6: Copyright © Texas Education Agency, 20131 Computer Programming Your First Java Program: HelloWorld.java

The main method

6. public static void main (String[] args)

Line 6 is the main method declaration.

A method contains programming statements.

Every Java application must have a “main” method.

(String[] args) is the parameter for the main method.

Parameters will be discussed in detail later.

Copyright © Texas Education Agency, 2013 IT: Beginning Computer Programming- First Java Program 6

Page 7: Copyright © Texas Education Agency, 20131 Computer Programming Your First Java Program: HelloWorld.java

Braces

7. {

Line 7 begins the main method with an opening curly brace({).

Braces enclose statements that make up a programming block.

Each opening brace must have a matching closing brace.

Copyright © Texas Education Agency, 2013 IT: Beginning Computer Programming- First Java Program 7

Page 8: Copyright © Texas Education Agency, 20131 Computer Programming Your First Java Program: HelloWorld.java

The main method

8. System.out.println ("Hello World!");

Line 8 prints a line of text.

The text that will be printed is enclosed in parentheses.

The statement ends with a semicolon.

“Hello World” is the text that will be displayed.

Text enclosed in quotes is called a string.

Copyright © Texas Education Agency, 2013 IT: Beginning Computer Programming- First Java Program 8

Page 9: Copyright © Texas Education Agency, 20131 Computer Programming Your First Java Program: HelloWorld.java

Closing Braces

9. }

10. }

Line 9 and 10 close the braces that were opened on lines 5 and 7.

Indenting is not necessary but helps to make the program more readable.

Copyright © Texas Education Agency, 2013 IT: Beginning Computer Programming- First Java Program 9

Page 10: Copyright © Texas Education Agency, 20131 Computer Programming Your First Java Program: HelloWorld.java

Running the Program

When you run the program,

Hello World!

Should display in the output window.

Copyright © Texas Education Agency, 2013 IT: Beginning Computer Programming- First Java Program 10

Page 11: Copyright © Texas Education Agency, 20131 Computer Programming Your First Java Program: HelloWorld.java

Introducing Errors

Programmers are always fixing errors.

We will explore a few types of errors:

Line 6: public static void main (String[] args)

Change it to: public static vod main (String[] args)

Compile and you will see the error:

“cannot find symbol class vod” – therefore you need to correct the spelling. This is a compile-time error.

Copyright © Texas Education Agency, 2013 IT: Beginning Computer Programming- First Java Program 11

Page 12: Copyright © Texas Education Agency, 20131 Computer Programming Your First Java Program: HelloWorld.java

Ending the Lesson

Play around making changes and noting the errors.

Do not introduce more than one error at a time!

Copyright © Texas Education Agency, 2013 IT: Beginning Computer Programming- First Java Program 12