当我写导入java.io. *时显示错误；

Question

why i am getting error when i write import java.io.*; in java file ?

dev_ps@DPS:~/Desktop/MorningDose$ javac dev.java
----------
1. WARNING in /home/dev_ps/Desktop/MorningDose/dev.java (at line 2)
    import java.io.*;
           ^^^^^^^

The import java.io is never used

Answer 1

With javac you're compiling your program, you're not running it!

after using the command javac dev.java a class file dev.class is created. If you have defined a main method in the java file you can execute the java-program with the command:

java dev

In order to understand the difference between compilation and execution you should defenetly read something about these two topics!

---

To your original question:

The import java.io is never used is a warning which tells you that you use no functionality from java.io . That means you can delete the line import java.io.*; (or any alike that isn't used) from your code!

Answer 2

It is warning you that you are not using the import, so it is useless. It will still run with this, but generally it is considered correct to only import what you use.

Answer 3

Its only a warning, Java compiler warning you because, your not using any class from java.io package. The good practice is remove all un used imports from your classes. Otherwise it will load all the classes while class load time when application start to execute.

Also if you want to load any class from other package declare only to specific class for eg: if your using BUfferedReader, use as follow

import java.io.BufferedReader;