Java_se Foundation--56. Package creation

Next I'll tell you ... Package

Look at a piece of code first

Class Demo1{public static void Main (string[] args) {System.out.println ("This is the main method of Demo1");}}

then create a new Java file, then the class name is also called Demo1, but the file is called Demo2

Class Demo1 {public static void main (string[] args) {System.out.println ("This is the main method of Demo2");}}

What if I compile Demo1 and then compile Demo2 and run the Demo1 result? Output: This is the main method of Demo1, or output: This is the main method of Demo2.

Operation Result:

This is the main method of Demo2.

Have you ever thought about why???

Because, after compiling this file is not also will produce demo1.class of this file after compiling will overwrite the previous compilation

Package: You can resolve the class name to repeat the problem.

The role of the package:

1. Resolve the problem of duplicate class names that create conflicts.

2. Easy release of software version.

Concept of package:

Is there a folder in Windows where you can't have two files of the same name, and how does that work in Windows? That is creating folders, so packages in Java are equivalent to Windows folders.

To define the format of the package:

Package name;

Things to note in a package statement:
1. The package statement must be in the first statement in a Java file.
2. If a class adds a package statement, the class's full class name is: Package name. class Name
3. A single Java file can have only one package statement.

The following section of code to create a package try:

Package A;class Demo1 {public static void main (string[] args) {System.out.println ("This is the main method of Demo1 ...");}

Then compile the results such as:

What's the meaning of this hint? Exception: Noclassdeffounderror; The meaning of the class name is not found

We look at the 2nd of matters to note in the package statement. The complete class name for this class is: A. Demo1

First create a folder called A, drag the demo1.class in,

And then run

New Folder method is not very annoying, then I continue to say another way ~

Javac-d the storage path of the specified class file Java source file

or javac-d. Java source file (. means the current folder path, which is the path of the Demo1)

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Java_se Foundation--56. Package creation