Common Java class libraries

1. stringbuffer class

Once declared, the string cannot be changed. If you want to change the string reference address, you must use

Stringbuffer class. In string, you can use "+" to connect strings. In stringbuffer, you must use the append method to connect strings.

2. runtime class

In Java, the runtime class indicates the runtime operation class. It is a class that encapsulates JVM processes. Each JVM corresponds to an instance of this runntime class.

It is instantiated when JVM is running. The instantiation method is as follows:

Runtime run = runtime. getruntime (); // uses the static method of the runtime class to instantiate it.

3. system class

The system class is a collection of system-related attributes and methods, and all attributes in the system class are static. to reference these attributes and methods, use them directly.

You can call the system class.

After a class is loaded and initialized, the object can be instantiated. The constructor is called to complete Object Instantiation. when an object is no longer in use, it will wait for garbage collection.

Collection, object termination, and finallyProgramUninstall.

4. Date operations

Date, calendar, dateformat, and simpledateformate

5. Math class

6. Random class

7. numberformat class

8. decimalformat class

9. biginteger class

10. bigdecimal class

11. Object cloning

12. arrays class

13. Comparable Interface

14. Regular Expression

15. Regular Scheduling