macOS Java Program Wont Compile

Robb.Penoyer said:

What error does the compiler give you.

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Robb.Penoyer said:

OK... I know this sounds like a goose chase... but could you post the entire stack trace? It helps set up context for us to help you analyze the problems.

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Exception in thread "main" java.lang.NoClassDefFoundError: Add2Integers/java
Caused by: java.lang.ClassNotFoundException: Add2Integers.java
	at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:315)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:330)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:250)
	at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:398)

mrbash said:

I'm not sure about the class you are extending, but ensure that it actually has the 'println' method. If not, you need to use 'System.out.println' instead.

I got this program code at this web site below. If you don't think it will take up to much of your time, my question is pertaining to this video starting at 15:47 – 18:57.

http://www.youtube.com/watch?v=NPzPnycCFuE&feature=SeriesPlayList&p=84A56BC7F4A1F852

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mrbash said:

I'm not sure about the class you are extending, but ensure that it actually has the 'println' method. If not, you need to use 'System.out.println' instead.

Also, you haven't declared the visibility of the class. Generally you would want 'public' visibility.

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import acm.program. *;
import acm.graphic. *;
    
     class Add2Integer extends consoleprogram {
         public void run() {
         public visibility;
     System.out.println("This program adds two numbers.");
          int n1 = readInt("Enter n1: ");
          int n2 = readInt("Enter n2: ");
          int total = n1 + n2;
          System.out.println("The total is " +total + ".");
       }
}

oneeach said:

There are a few points that I need to make before answering the original question.

1. This code is based on a package designed to help ease the learning curve of Java. The problem with this approach is that most of us don't use that library (ConsoleProgram is actually acm.program. ConsoleProgram which I have never seen before)

2. The compiler (javac) is used to convert a .java file into a .class file. This is done before the program executes. I'm guessing you are using an IDE such as Eclipse or NetBeans which compiles automatically for you.

3. The stack trace is actually from running the program, not compiling it. It does compile, it just doesn't run correctly.

There are two hints as to what the problem is. The first is the "Exception in thread "main" java.lang.NoClassDefFoundError: Add2Integers/java" message most notably the "Add2Integers/java" on the end. The next is the very next line "Caused by: java.lang.ClassNotFoundException: Add2Integers.java" Remember, in Java the full class name includes the package with periods between the names. You can also put a class inside of a class. For example, if you added "class Foobar" inside of Add2Integers the it would be "Add2Integers.Foobar".

Now look at the second line of the stack trace. Notice that it says it cannot find "Add2Integers.java"? Somewhere, you told it to run with Add2Integers.java and it is looking for "class java" inside of Add2Integers. To fix it, change the way you start the program with just Add2Integers instead of Add2Integers.java.

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import acm.program. *;
import acm.graphic. *;
    
   class Add2Integer extends graphicsprogram {
          public void run() {
          println("This program adds two numbers.");
          int n1 = readInt("Enter n1: ");
          int n2 = readInt("Enter n2: ");
          int total = n1 + n2;
          System.out.println("The total is " + total + ".");
       }
}

mrbash said:

There are two things I see.

I am not sure if you are have incorrectly copy/pasted the code, but if you have accurately copied the code in the above message, there are a few things I would fix:

HTML:

import acm.program.GraphicsProgram;
    
   public class Add2Integer extends GraphicsProgram {
          public void run() {
          println("This program adds two numbers.");
          int n1 = readInt("Enter n1: ");
          int n2 = readInt("Enter n2: ");
          int total = n1 + n2;
          println("The total is " + total + ".");
       }
}

The reason the BlueJ IDE is complaining about the package "acm.program" is probably because you haven't added the acm library to your project yet. Locate the "jar" file that is the ACM library and copy it into the BlueJ/lib directory. I'm familiar with the BlueJ IDE but the internet tells me that's where you place your library files.

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wrldwzrd89 said:

Also, check the run settings for your program in BlueJ. Do you have it set to launch "Add2Integer.java" instead of "Add2Integer"? That will cause this error, because the Java interpreter thinks you're trying to specify a package name, and cannot find it.

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chown33 said:

Java is case-sensitive. I've hilited your spelling error in red.


Earlier:

Code:

import acm.program. *;
import acm.graphic. *;
    
   class Add2Integer extends [COLOR="Red"]graphicsprogram[/COLOR] {

The spelling error is in red again.

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