A Short Introduction to Writing Java Code. Zoltán Majó

Transcription

1 A Short Introduction to Writing Java Code Zoltán Majó

2 Outline Simple Application: Hello World Compiling Programs Manually Using an IDE Useful Resources

3 Outline Simple Application: Hello World Compiling Programs Manually Using an IDE Useful Resources

4 Hello World Learning a new programming language usually starts with Hello World: Using your favorite editor save as HelloWorld.java

5 About Text Editors Generally it is good to learn a feature-rich editor Our recommendation: Emacs You can use whatever editor you like (notepad, vim, gedit, jedit, etc.)

6 Where to Save? It is a good idea to save to NAS storage offered by ID, available in all student rooms Windows: mapped as drive T: Linux: mounted in /CIFS/ /<nethz_id> Personal data should be stored in private Service documentation: tud/homeverzeichnis/index_en

7 Outline Simple Application: Hello World Compiling Programs Manually Using an IDE Useful Resources

8 Compiling Change directory to that of the source file Compile with command: javac HelloWorld.java Classfile containing bytecode: HelloWorld.class Run the program: java HelloWorld

9 Using the Compiler Open Command Prompt (Windows) or Terminal (Linux) Windows: PATH=%PATH%;<path to jdk>\bin eg. PATH=%PATH%;c:\Program Files\Java\jdk1.6.0_11\bin Linux: export PATH=$PATH:<path to jdk>/bin

10 Using the Compiler Open Command Prompt (Windows) or Terminal (Linux) Windows: PATH=%PATH%;<path to jdk>\bin eg. PATH=%PATH%;c:\Program Files\Java\jdk1.6.0_11\bin Linux: export PATH=$PATH:<path to jdk>/bin

11 Using the Compiler Open Command Prompt (Windows) or Terminal (Linux) Windows: PATH=%PATH%;<path to jdk>\bin eg. PATH=%PATH%;c:\Program Files\Java\jdk1.6.0_11\bin Linux: export PATH=$PATH:<path to jdk>/bin

12 Some Words About Java Technology Why don t we run the executable directly, why invoke it within another program (java)? Java is compiled to Java bytecode, an intermediate binary format Then, the Java Virtual Machine executes the bytecode Source Code Bytecode Native code Java compiler (javac) Java Virtual Machine (java)

13 Some Words About Java Technology Why don t we run the executable directly, why invoke it within another program (java)? Java is compiled to Java bytecode, an intermediate binary format Then, the Java Virtual Machine executes the bytecode Source Code Bytecode Native code Java compiler (javac) Java Virtual Machine (java)

14 Some Words About Java Technology Why don t we run the executable directly, why invoke it within another program (java)? Java is compiled to Java bytecode, an intermediate binary format Then, the Java Virtual Machine executes the bytecode Source Code Bytecode Native code Java compiler (javac) Java Virtual Machine (java)

15 Some Words About Java Technology Why don t we run the executable directly, why invoke it within another program (java)? Java is compiled to Java bytecode, an intermediate binary format Then, the Java Virtual Machine executes the bytecode Source Code Bytecode Native code Java compiler (javac) Java Virtual Machine (java)

16 Organizing Project Good idea to separate sources, binary files, documentation Example layout: Compile with: javac d bin src\helloworld.java Execute with: java cp bin HelloWorld

17 Outline Simple Application: Hello World Compiling Programs Manually Using an IDE Useful Resources

18 Eclipse IDE Good news: Eclipse can do all these for you automatically Workflow: create workspace create project create main class run

19 Setting up the Workspace Advice: use your network share, because the format of the project directory is platformindependent

20 Creating a Project

21 Creating a Project Please note that separate source and class folders are used If using the same workspace on multiple machines, please make sure that the compliance level is the same you are using the same version of Eclipse

22 Creating a Project Please note that separate source and class folders are used If using the same workspace on multiple machines, please make sure that the compliance level is the same you are using the same version of Eclipse

23 Creating a Project Please note that separate source and class folders are used If using the same workspace on multiple machines, please make sure that the compliance level is the same you are using the same version of Eclipse

24 Creating the Main Class

25 Creating the Main Class

26 Creating the Main Class

27 Creating the Main Class

28 Writing the Program Add the call to System.out.println() to the method body

29 Running the Program Click on Ctrl + F11 to run the application or press Results should be observed below, in the console window

30 Useful Links Java: Eclipse: Emacs: Java Tutorial: Java Code Conventions: Java API: