在Java中打开文件后会发生什么

Question

suppose that using a JFilechooser , we choosed a text file which contained 1 line , say... "hello world"

File file = new File("someFile.txt")

when we print the file contents we get "hello world" but what happens if we changed the text file contents and added some new lines , and printed again , does java stores the file in memory ? or it will reads it again , and consequently prints the new lines we added ?

Answer 1

That depends on what you do. The rules are simple: when you read it again by using a FileInputStream or a FileReader , you will always get the latest content. The OS might optimize this in memory, if the file is not edited. If you simply keep the file contents into a self constructed buffer (eg: a String or a byte[] ), and the file changes, of course the buffer will remained unchanged.

Answer 2

When you create a File , nothing actually happens. The location of the file is stored, nothing else. It's like setting your GPS to go somewhere versus driving there.

From the Javadoc:

An abstract representation of file and directory pathnames.

When you read from the file, you'll get the contents of the file.