☞Collection of predefined classes is known as java library.
☞How to use? :-either inherit them or instantiate them.
☞These are classes inside dynamically,loadable libraries that Java applications can call at any time.
☞Example :- In java.lang.Math, Math is a class which is inside the java.lang package.
☞Java resides in mobiles ,client machines,server machines, embedded devices,smart phones,cloud etc.
☞Principle of Java : Write Once, Run Anywhere(WORA)