- Data represents information.
- Input refers to the data provided to the computer program for processing and the program generates the output after processing and displays onto the monitor.
- Generally the input is given to the program through input source such as keyboard, mouse or as a file.
- The output is displayed onto the monitor as an action.
- The flow of data from one place to another is called stream.
- The flow of data from the input source to the program for processing is called input stream.
- Input stream is used to read the data from the source.
- The flow of data from the program to the monitor or the destination is called output stream.
- Output stream is used to write data.
- Java.io package contains classes which handle the input and output streams.
The System Class:
The system class is a final class under Java.lang package and cannot be instantiated. It has three fields which are static, they are in, out and err.
- System.in represents Inputstream object. This input stream refers to the input source specified by the user (eg) Keyboard.
- System.out represents Outputstream object. This output stream is used to display the output onto the destination specified by the user such as monitor, etc.
- System.err represents Outputstream object. This output stream is used to display error messages onto the monitor.