Java builder

The Java builder builds Java programs using a compiler that implements the Java Language Specification.  The Java builder can build programs incrementally as individual Java files are saved.

Problems detected by the compiler are classified as either warnings or errors. The existence of a warning does not affect the execution of the program; the code executes as if it were written correctly. Compile-time errors (as specified by the Java Language Specification) are always reported as errors by the Java compiler. For some other types of problems you can, however, specify if you want the Java compiler to report them as warnings, errors or to ignore them. To change the default settings, use the Window > Preferences > Java > Compiler preference page.

The Java compiler can create CLASS files even in presence of compilation errors. However, in the case of serious errors (for example, references to inconsistent binaries, most likely related to an invalid build path), the Java builder does not produce any CLASS files.

Build classpath
Java development tools (JDT)

Building a Java program
Building automatically
Building manually
Viewing compilation errors and warnings
Working with build paths Viewing and editing a project's build path
Adding a JAR file to the build path
Adding a library folder to the build path

Java Build Path properties
Java Compiler preferences