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Java is a compiled language instead of interpreted. That means that running Java code is a two-step process: first the code is compiled, which creates .class files. Then, those .class files are executed, running the actual code. To do this in the command line, type these two commands:
$ javac *.java $ java CodeToRun $
The first line compiles all the code in files that have the .java suffix. If there are any syntax errors, they will be reported and the compilation will fail. The second line executes the file CodeToRun.class. (The .class designation is left off when running Java.) Everytime you change the source code (don't forget to save it!) you need to recompile it to get the new executable .class files.
Let's introduce an error to see what a syntax error looks like: (I misspelled the word class in the first line)
public clas CodeToRun {
//code inside the class. (This is a comment.)
}
$ javac *.java
CodeToRun.java:1: error: class, interface, or enum expected
public clas CodeToRun {
^
CodeToRun.java:5: error: class, interface, or enum expected
}
^
2 errors
$
Java reported two errors. Important:Only worry about the first one! In many cases, fixing the first error will solve many of the later ones. In this case, Java found an syntax error on the first line, so it ignored that line. That causes the last line to also have a problem, because Java detects what looks like an extra close-squiggly brace. Notice that the compiler points out the first character of the symbol (clas in the first error) where it notices each error.
Add the second 's' back, recompile and run the code to make sure everything is working again before continuing.
main MethodsNothing is output here because there's nothing to run inside CodeToRun.java. When a .class file is executed, Java automatically calls the main method inside that class. Without the main method, nothing happens. Let's add a main method now:
public class CodeToRun {
public static void main(String[] args) {
//code will go in here (this is a comment)
}
}
Compile and run this code again. Nothing still happens, since there's nothing to execute inside the main method. Next we'll add some code that will actually execute!
Update your Monkey.java to include a main method. Compile and run your file. (You shouldn't get any output.)