3 major steps for creating/running a java program you write the source code for the program and save...

3 Major Steps for Creating/Running a Java Program

• You write the source code for the program and save it as a .java file.

• You compile the .java program using the compiler (javac). When you compile, it checks for syntax errors. When it successfully compiles, it creates a java bytecode file that ends in .class

• You interpret and execute the bytecode using the interpreter (the Java Virtual Machine, java)

IDE• IDE stands for Integrated Development Environment. • It is basically a fancy text editor that gives you easy access to

the compiler and interpreter• If you get an IDE, you still have to download the JDK before

you can use it• Although there are better IDEs out there, some of them are

kind of complicated (like Oracle's NetBeans IDE and the Eclipse IDE) and others cost money (like developer versions of IDEs like JBuilder), so to make it easier we are going to use a useful, free, and easy one called JCreator

• If you want to try Oracle's NetBeans, you can download the "bundle" on the same page that you download the JDK from


public class CompSci{

}

All Java programs start with a class.


public class CompSci{ public static void main(String[] args) { System.out.println("Comp Sci!"); }} OUTPUT

Comp Sci!


public class CompSci{ //open brace

public static void main(String[] args) { System.out.println("Comp Sci!"); }} //close brace

Braces – You gotta have ‘em! Every classand every method must have a { and a } .


public class CompSci{ public static void main(String[] args) { System.out.println("Comp Sci!"); }}You must put a semi-colon at the end of all Java program statements ( ; ).


Never put a ; before an open { brace

;{ //illegal}; //legal


public class CompSci{ public static void main(String[] args) { System.out.println("Comp Sci!"); }}

Indent all code 3 spaces to make it easier to read.


System.outfrequently used methods

Name Use

print(x) print x and stay on the current line

println(x) print x and move to next line down

printf(s,x) print x according to s specifications


System.out.print("compsci");

reference command / method

OUTPUTcompsci


System.out.print("compsci");System.out.print("compsci");

OUTPUTcompscicompsci


System.out.println("compsci");

OUTPUTcompsci


System.out.println("compsci");System.out.println("compsci");

OUTPUTcompscicompsci


System.out.println("c\tompsci");

\n newline\t tab\r carriage return\b backspace

OUTPUTc ompsci


System.out.println("com\tpsci");

OUTPUTcom psci



System.out.println("comp\nsci");

OUTPUTcompsci



\\ outs \\" outs "\’ outs ’

System.out.println("\\compsci\"/");

OUTPUT\compsci"/


\\ outs \\" outs "\’ outs ’

System.out.println("\\'comp\'sci\'/");

OUTPUT\'comp'sci'/


Escape Sequencesfrequently used combinations

Name Use

\t tabs over five spaces

\n moves to front of next line

\b deletes previous character

\r moves to front of current line

\\ nets one backslash \

\" nets one double quote "

\’ nets one single quote ’


// single-line comments/* */ block comments

//this line prints stuff on the screenSystem.out.println("stuff");


// single-line comments/* */ block comments

/* this line prints stuff on the screen*/System.out.println("stuff");


System.out.printf("%s","compsci\n");

OUTPUTcompsci


Syntax errors occur when you type something in wrong, causing the code to not compile.

//missing semicolon - ; expectedSystem.out.println("stuff")

//case problem – should be Systemsystem.out.println("stuff");


Runtime errors occur when something goes wrong while the program is running.

//an out of bounds exception is thrownString s = "runtime_error";System.out.println( s.charAt(15) );

Importing

• There is a whole bunch of code already written for Java and included with it...why start from scratch with each program?

• To use pre-existing code, you need to import the class (ie, the file containing the code) at the top.

• To see a list of existing classes that you can use, go to the Java API (Application Program Interface)http://download.oracle.com/javase/7/docs/api/

• You can think of the classes in the API as building blocks you can use to make your programs

• The JOptionPane class is for simple GUIs...we'll use much more of it and many API classes in the future

http://download.oracle.com/javase/7/docs/api/

Importing in Acition

3 major steps for creating/running a java program you write the source code for the program and save...

Documents

computer science

class compsci

java file

java programyou

java programs

printlncomp sci

java bytecode file

java program statements