How android apps use library made by user?

I was reading one of the articl开发者_开发知识库es on internet and he was saying that he'll make library so that all the apps can use it. How is this possible? Any ideas?

To add libraries to your project, in eclipse package manager right click on your project select 'Properties' on the left select 'Java Build Path' then click on the libraries tab toward the top. Click the 'Add External Jars' button navigate to the jarfile and select it. Then you are ready to import and use whatever was inside of it in your project. I recommend you add a libs folder to your project and keep all of the jar files used in that project inside there so that if you distribute your project source to someone else they will have all of the needed libraries to compile it.