How to use the command prompt to work with Java

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How to use the command prompt to work with Java

If you're using TextPad, you can use its commands to compile and run most of your Java applications. Even so, there may be times when you will need to compile and run Java applications from the command prompt. And if you're using another text editor that doesn't provide compile and run commands, you can use the command prompt to compile and run all of your Java applications.

How to compile source code

Figure 1-12 shows how to use a command prompt to compile and run applications. In particular, this figure shows how to use the Windows command prompt, sometimes called the DOS prompt.

To start, you enter the change directory (cd) command to change the current directory to the directory that holds the application. In this figure, for example, you can see that the directory has been changed to c:\java\examples\ch01 because that's the directory that contains the TestApp.java file. Then, to compile the application, you use the javac command to start the Java compiler. When you enter the javac command, you follow it by a space and the complete name of the .java file that you want to compile. Since Java is case-sensitive, you need
to use the same capitalization that you used when you saved the .java file.

If the application doesn't compile successfully, you can use your text editor to correct and resave the .java file, and you can compile the program again. Since this means that you'll be switching back and forth between the text editor and the command prompt, you'll want to leave both windows open.

When you compile an application successfully, the Java compiler will create a .class file that has the same file name as the .java file. For example, a successful compilation of the TestApp.java file will create the TestApp.class file. This .class file is the file that contains the Java bytecodes that can be run by the Java interpreter.

Introduction to Java ...................................................................... 4
Toolkits and platforms ....................................................................... 4
Java compared to C++ ...................................................................... 4
Java compared to C# ........................................................................ 4
Applications, applets, and servlets ....................................................... 6
How Java compiles and interprets code ................................................ 8
How to prepare your system for using Java .................................. 10
How to install the JDK ..........................................................................10
A summary of the directories and files of the JDK ...................................12
How to set the command path ...............................................................14
How to set the class path ..................................................................... 16
How to use TextPad to work with Java ........................................... 18
How to install TextPad ......................................................................... 18
How to use TextPad to save and edit source code ................................... 20
How to use TextPad to compile source code ........................................... 22
How to use TextPad to run an application ............................................... 22
Common error messages and solutions ................................................. 24
How to use the command prompt to work with Java ...................... 26
How to compile source code ................................................................. 26
How to run an application ..................................................................... 26
How to compile source code with a switch .............................................. 28
Essential DOS skills for working with Java ............................................. 30
How to use the documentation for the Java SE API ....................... 32
How to install the API documentation ..................................................... 32
How to navigate the API documentation ................................................. 34
Introduction to Java IDEs ................................................................ 36
The Eclipse IDE for Java ....................................................................... 36
The NetBeans IDE ................................................................................ 38
The BlueJ IDE ...................................................................................... 38
Perspective ....................................................................................... 40

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How to run an application

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How to run an application

To run a program from the command prompt, you use the java command to start the Java interpreter. Although you need to use the proper capitalization when you use the java command, you don't need to include an extension for the file. When you enter the java command correctly, the Java interpreter will run the .class file for the application.

Running a Java program often displays a graphical user interface like the one shown in figure 1-2. However, you can also print information to the console and get input from the console. For example, the TestApp file in this figure prints a single line of text to the console.

The commands for compiling and running an application

Syntax to compile an application

javac ProgramName.java

Syntax to run an application

java ProgramName

Description

• The command prompt is the prompt that indicates that the operating system is waiting for the next command. This prompt usually shows the current directory, and it always ends with >.
• In Windows, the command prompt is sometimes referred to as the DOS prompt or theDOS window. You can enter DOS commands at the DOS prompt.

Operation

• To open a command prompt in Windows, click on the Start button, find MS-DOS Prompt or Command Prompt, and select it. If its location isn't obvious, try looking in Accessories.
• To change the current directory to the directory that contains the file with your source code, use the change directory command (cd) as shown above.
• To compile the source code, enter the Java compile command (javac), followed by the file name (including the java extension). Since this is a case-sensitive command, make sure to use the same capitalization that you used when naming the file.
• If the code compiles successfully, the compiler generates another file with the same name, but with class as the extension. This file contains the bytecodes.
• If the code doesn't compile successfully, the java compiler generates error messages for the compile-time errors. Then, you must switch back to your text editor, fix the errors, save your changes, and compile the program again.
• To run the compiled version of your source code, enter the Java command (java), fol lowed by the program name (without any extension). Since this is a case-sensitive command, make sure to use the same capitalization that you used when naming the file.

Note

• The code shown in the command prompt above will only work if the bin subdirectory of the JDK 6 directory has been added to the command path as shown in figure 1-6.
  

Introduction to Java ...................................................................... 4
Toolkits and platforms ....................................................................... 4
Java compared to C++ ...................................................................... 4
Java compared to C# ........................................................................ 4
Applications, applets, and servlets ....................................................... 6
How Java compiles and interprets code ................................................ 8
How to prepare your system for using Java .................................. 10
How to install the JDK ..........................................................................10
A summary of the directories and files of the JDK ...................................12
How to set the command path ...............................................................14
How to set the class path ..................................................................... 16
How to use TextPad to work with Java ........................................... 18
How to install TextPad ......................................................................... 18
How to use TextPad to save and edit source code ................................... 20
How to use TextPad to compile source code ........................................... 22
How to use TextPad to run an application ............................................... 22
Common error messages and solutions ................................................. 24
How to use the command prompt to work with Java ...................... 26
How to compile source code ................................................................. 26
How to run an application ..................................................................... 26
How to compile source code with a switch .............................................. 28
Essential DOS skills for working with Java ............................................. 30
How to use the documentation for the Java SE API ....................... 32
How to install the API documentation ..................................................... 32
How to navigate the API documentation ................................................. 34
Introduction to Java IDEs ................................................................ 36
The Eclipse IDE for Java ....................................................................... 36
The NetBeans IDE ................................................................................ 38
The BlueJ IDE ...................................................................................... 38
Perspective ....................................................................................... 40

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