How to Build Your Own Java library?

Code reuse is one of the most important factors in software development. It is a VERY good idea to put frequently-used functions together and build a library for yourself. Whenever some method is used, just simply make a method invocation. For Java, it's straightforward to manage such a library. Here a simple example in Eclipse. The library will contain only one "add" method for demo purpose.

Step 1: Create a "Java Project" named as "MyMath", and a simple "add" method under "Simple" class.

Package structure is as follows:

public class Simple {
	public static int add(int a, int b){
		return a+b;

Step 2: Export as a .jar file.

Right Click the project and select "export", a window is show as follows.

Following the wizard, to get the .jar file.

Step 3: Use the jar file.

Right click the target project, and select "Build Path"->"Add External Archives"->following wizard to add the jar file.

Now you can make a simple method call.

public class Main {
	public static void main(String[] args) {
		System.out.println(Simple.add(1, 2));

Last, but not the least, the library should be constantly updated and optimized. Documentation is important. If the library is not documented well, you may totally forget a function you programmed a year ago. Proper package names should be used to indicate the function of classes and methods. For example, you can name first layer of the packages by following the package names of standard Java library: programcreek.util,, programcreek.math, programcreek.text, etc. You domain specific knowledge then can be used in the next level. In addition, always do enough research first and make sure there is no implements of what you want to do before you start program anything. Libraries from industry utilizes the power of thousands of smart developers.

Category >> Basics  
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  • i have advice for your curiosity. if you want to know how to it manually you can look it from terminal IDE. My IDE Netbeans has terminal or output to show what IDE doing when build it. I hope this fill your knowledge

  • Jivey

    This question still boggles my head in my 3rd year of uni. I can compile to jar in the terminal but that’s not exactly the same as a JRE library. Java has changed lots, more tools have come out, and Java has always been very customizable considering its an OOP. I will reply here should I ever figure it out. No, I don’t want to use a wizard, we are devs not script kiddies.

  • Jivey

    How would I do this without the wizard? Like if I were using sublime or wanted to understand it manually.

  • Poon

    Could I ask why the Library can only be used once per class? Whenever I try to reuse it java.util.NoSuchElementException comes up. Thanks

  • Suq madiq


  • Nice and straight to the point