Attaching source of any Jar in Eclipse e.g. JDK or open source libraries like
Spring framework is good idea because it help during debugging and code development.
As a Java programmer at least you should attach source of JDK in Eclipse IDE to
find out more about JDK classes. Though Eclipse IDE is pretty good on code
assist, sometime You want to know what's going inside a library or a JDK method,
rather than just reading documentation. Interview questions like How
HashMap works in Java or How
substring cause memory leak can only be answered if you are familiar with source
code of these classes. Once you attach
source code of Java or Spring in Eclipse IDE, You can check code with just a
single click. Some one may argue for Java decompiler like JAD which can create
source from .class
file which is also a smart way to look code for open source library, but
decompiled source file is not same as original source file, as you lost comment
and readability. As per my experience attaching source code corresponding to
JAR file is much better than decompiling a class file using JAD decompiler.
As I said when you attach source code for any JAR file, You not only see properly formatted code but also all the code comments which is not available if you are decompiling class file. But at same time its not possible to attach Java source code of every single library in Eclipse. So combination of both decompiler and source code attachment in Eclipse is best way to go. As I have always argued for learning Eclipse keyboard shortcuts and Eclipse settings to improve productivity e.g. save action, this is also one of the Eclipse tips which will help you during development and debugging in Java. In this Eclipse tutorial we will see How to attach source code for any JAR in Eclipse and we will attach source code of JDK by following steps given in this tutorial.
Attaching source code of JDK in Eclipse IDE
There are multiple ways to attach source in Eclipse for any JAR file, but
I found following approach as most simple one because it attach code directly
to the JAR file by right clicking ot it.
1. Select any Java project
2. Expand Referenced libraries
3. Select any JAR file, in our case rt.jar which is Java runtime
4. Right click and go to properties
5. Attach source code by browsing source path.
After performing above 4 steps following window will appear where you can
browse source code for any JAR file. In our case source code for rt.jar is
src.zip which can be found in JAVA_HOME
directory or JDK installation directory in your computer.
Now let’s see What difference attaching source code in Eclipse makes.
Suppose you want to see code of HashSet
class to find out How HashSet works in Java or source code of java.lang.String class to
find out internal implementation of String class. Let’s use Eclipse shortcut to find any Type e.g. ctrl+T and select
java.lang.String class. If you don’t have source code attached for rt.jar or JDK, as
java.lang.String belongs to rt.jar , it will display
java.lang.String class in class file editor as shown below.
Once you attach source code in Eclipse for JDK by following above steps,
select java.lang.String again. This time you will see
proper source for String class from rt.jar as shown
in following pic.
That’s all on How to attach source code in Eclipse for any JAR for
debugging or code lookup purpose. I personally add source code of JDK and frequently used library like
Spring, Hibernate or Apache commons and leave rest of JAR for decompiler to
take care of. You can attach source code for even your in house libraries which
is quite common in Investment banks.
Related Eclipse Tutorials for Java programmers
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