Dark Horse Programmer _ Package, access modifier, and inner class

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A. Package:

1. Define Package usage keywords: packages;

1). Precautions:

The A.package statement must be the first executable code of the Java source program

The B.package statement can have only one in a Java file

C. If there is no package, default means no packages name

2. Import package using keywords: import;

1). Precautions:

A. Import into the final class;

B. Wildcard characters can be used: *, only the class under the package, not including other classes under the sub-package;

C. In a class file, you can have more than one import statement;

The D.import statement must precede the package statement before the class is defined;

3.package,import,class have a sequential relationship?

There are: Package-->import-->class

Two. Access modifiers:

1. To qualify "class" and "member" to be accessed by other classes under other packages;

2. Four access modifiers:

1). Public: You can decorate classes, members. can be accessed by any other class under any package;

2). protected (Protection): Members can be decorated. can be accessed by other classes under the same package. If only the quilt class access outside the package;

3). (default): Class, member can be decorated. can only be accessed by other classes within the package;

4). Private (private): Members can be decorated. can only be accessed by other methods in the class;

3. Modifiers available for classes and members:

1). Class: (default), public,final,abstract our own definition: public mostly

2). Member variables: Four permission modifiers are available, final,static we define: private majority

3). Construction method: Four kinds of permission modifiers are available, others can not be defined by us: public majority

4). Member Method: Four permission modifiers are available, fianl,static,abstract we define: public mostly

Three. Inner class:

1. member Inner class:

1). defined in the class body, as a member of the class;

2). You can use the same modifier as the "member method" of the same class;

2. Local Inner class:

1). Defined within a method or block of code;

2). You cannot use the "access modifier", you cannot use the static modifier; You can use the final and abstract

3). Note: Local internal classes access "local variables", requiring local variables to be final (constants);

Class a{

public void Show () {

int num = 10;//This variable requirement must be: final

Class b{

public void Method () {

SYSTEM.OUT.PRINTLN ("num =" + num);//Compilation error

}

}

}

}

3. Anonymous inner class:

1). is a simplified notation of the inner class.

2). Premise: There is a class or interface here the class can be either a concrete class or an abstract class.

3). Format: New class name or interface name () {override method;}

4). Nature: A subclass of anonymous objects that inherit a class or implement an interface

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Dark Horse Programmer _ Package, access modifier, and inner class