Java Private

Java Private
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The keyword ‘private’ in Java is used to establish the limitation of accessibility of the class, method or a variable in the java code block. If a class, method or variable is entitled as private in the program, that means that a particular class, method or variable cannot be accessed by outside the class or method, unlike the public method. The Private keyword is typically used in Java in a fully encapsulated class.
Private Keyword in Java works within a particular class. It can’t be accessed outside of the class. It doesn’t work outside the class/classes and interface/ interfaces. Private Keyword works well if the members of the class are PRIVATE and that too in a fully encapsulated class. Private Keyword or variable or method can also be overridden to the sub-class/classes using some access modifiers to invoke PRIVATE METHOD outside of the class. With this, Private Keyword also works outside of the class only using the Private Access Modifiers.
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Here are some examples of private modifiers, which are as follows:
Here we are illustrating the example of Private Access Modifier, which shows compilation error because of private data member accessing from the class AB, which is shown in the below example. Private methods or Private members can only be accessible within a particular class.
This is an example of illustrating the use of the PRIVATE keyword with the program below:
Here in this example, you can see how the PRIVATE METHOD is overridden to the sub-class using the access modifier, which is the default. We are not even allowed to invoke the parent class method/methods from the sub-class.
Here in this example, I am illustrating that the PRIVATE METHOD cannot be invoked/called outside of the class. Here now, the private method is calling from the Outside class by changing class runtime behavior.
This is an example of a private method and field in Java Programming Language . Here private method/methods use static binding at the compile-time, and it even can’t be overridden. Don’t confuse with the Private variable output because the Private variable is actually accessible inside the inner class/classes. If PRIVATE variable/variables are invoked/called outside of the class, definitely the compiler will produce an error.
Here we are going to explain the advantages of using Private methods/fields in Java below.
Here are some rules and regulations for private that you should know.
Coming to the end of the main topic, we actually happy to know how helpful and easy using Private Keyword in Java. In this article, I hope you understand the private keyword, private variable, access modifier, private constructor, and how to use these private keywords in programs.
This is a guide to a Private constructor in java. Here we discuss the basic concept, working, advantages, rules, and private regulations in java and their examples and implementation. You may also look at the following articles to learn more –
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Yes, we can declare a class as private but these classes can be only inner or nested classes. We can’t a top-level class as private because it would be completely useless as nothing would have access to it.
private class Main
{
public static void main(String[] args) {
System.out.println("Inside private class");
}
}
Main.java:1: error: modifier private not allowed here
private class Main
^
1 error
private class Show{
void display(){
System.out.println("Inside display method.");
}
}
public class Main
{
public static void main(String[] args) {
Show show = new Show();
show.display();
}
}
Main.java:1: error: modifier private not allowed here
private class Show{
^
1 error
class Display {
//Private nested or inner class
private class InnerDisplay {
public void display() {
System.out.println("Private inner class method called");
}
}
void display() {
System.out.println("Outer class (Display) method called");
// Access the private inner class
InnerDisplay innerDisplay = new InnerDisplay();
innerDisplay.display();
}
}
public class Main { public static void main(String args[]) {
// Create object of the outer class (Display)
Display object = new Display();
// method invocation
object.display();
}
}
Outer class (Display) method called
Private inner class method called
private class Main
{
public static void main ( String [ ] args ) {
System . out . println ( "Inside private class" ) ;
}
}
Main. java : 1 : error : modifier private not allowed here
private class Main
^
1 error
private class Show {
void display ( ) {
System . out . println ( "Inside display method." ) ;
}
}
public class Main
{
public static void main ( String [ ] args ) {
Show show = new Show ( ) ;
show. display ( ) ;
}
}
Main. java : 1 : error : modifier private not allowed here
private class Show {
^
1 error
class Display {

//Private nested or inner class
private class InnerDisplay {
public void display ( ) {
System . out . println ( "Private inner class method called" ) ;
}
}

void display ( ) {
System . out . println ( "Outer class (Display) method called" ) ;
// Access the private inner class
InnerDisplay innerDisplay = new InnerDisplay ( ) ;
innerDisplay. display ( ) ;
}
}

public class Main {

public static void main ( String args [ ] ) {
// Create object of the outer class (Display)
Display object = new Display ( ) ;

// method invocation
object. display ( ) ;
}
}
Outer class ( Display ) method called
Private inner class method called

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I am given a class that has a private method say setCoors(int x, int y). The constructor of that class has the setCoors in it too. In a different class, I want to have a method setLocation which calls setCoors. Is this possible?
If I am not allowed to set the method to public, is this possible?
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The best and most helpful answer depends on the context of the question, which is, I believe, not completely obvious.
If the question was a novice question about the intended meaning of private, then the answer "no" is completely appropriate. That is:
Now, if , and okay maybe this is a stretch (thank you Brian :) ), that the question came from a more "advanced" context where one is looking at the question of "I know private means private but is there a language loophole", then, well, there is such a loophole. It goes like this:
Of course, this really isn't something that application programmers would ever do. But the fact that such a thing can be done is worthwhile to know, and not something that should be ignored. IMHO anyway.
No, private means the method can only be called inside of the Class in which it is defined. You will probably want to have setLocation create a new instance of the class setCoords resides in, or change the visibility on setCoords .
EDIT: The code you have posted will work. Just be aware that any instance of the Location class will be bound to its own Coordinate object. If you create a new Coordinate object somewhere else in your code, you will be unable to modify its internal state. In other words, the line
will create the object myCoord which will forever have the coordinates 4 and 5 .
If you want other classes to call it, maybe you shouldn't make it private?
No private methods can't be accessed outside the class in which they are defined
Kid-doing-homework: the answer is no. Guy-requiring-some-crazy-work-around-for-his-job: the answer is yes. Far more importantly though, Your setCoors method should not take int arguments. It should take two SilverBullet objects.
private means you can only access it inside the class defined.
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【Java】アクセス修飾子privateの使い方【クラス・メソッド・フィールド】

Javaではクラスやメソッド・フィールドの前にアクセス修飾子(private・public・protected)を付与することで、データにアクセス出来る範囲を指定します。
本記事では、Java初心者の方向けにアクセス修飾子privateの使い方をクラス・メソッド・フィールドでサンプルコードを掲載しながらご紹介していきます。

アクセス修飾子の1つである「private」は、同一クラス内でのみデータにアクセスすることが可能となります。
privateのアクセス範囲と同様に「public」「protected」「指定なし」の場合のアクセス範囲についても確認しておきましょう。

指定なしというのは「void メソッド名」のように、アクセス修飾子の指定をせず定義することを意味しています。

privateクラスは、他の外部クラスから呼び出されたくないクラスを定義する際に記述します。
内部クラスを定義する場合、1つのファイルにプログラムが増加する傾向にあり、privateクラスが利用される機会はそれほど多いわけではありません。
「Sample」クラスに定義した「PrivateSample」クラスを呼び出すサンプルコードが下記となります。
下記のように外部のクラスからprivateクラスを呼び出そうとするとコンパイルエラーとなります。
「型 Main.PrivateSample は不可視です」のエラーとなりコンパイルが出来ません。

privateメソッドはクラス内部でのみ使用したい処理を記述する際に利用します。
同一クラス内のmainメソッドから直接privateメソッドを呼び出すパターンと、外部クラスのprivateメソッドをpublicメソッドを経由して呼び出す2つのパターンを実行するサンプルです。
「privateSample1」のメソッドに関しては、呼び出し元の「main」メソッドと同一クラス内に存在するため問題なく処理を呼び出すことが出来ます。
外部クラスの「Sample」に記述している「privateSample2」に関しては「publicSample」を経由することで処理を実施しています。
では上記サンプルで「privateSample2」を直接「main」メソッドから呼び出す記述に変更してみましょう。
「メソッド privateSample2(String) は型 Sample で不可視です」のエラーとなりコンパイルが出来ません。

privateフィールドは、外部から直接フィールド値を変更してもらいたくない場合に利用します。
Javaのシステム開発では、基本的にメンバー変数であるフィールドはprivateに設定し、ゲッター(getter)・セッター(setter)と呼ばれるアクセス用のメソッドを公開する方法が一般的です。
外部クラスから値を変更したい場合は、セッターメソッドを呼び出し値を変更した上でゲッターメソッドで値を取得するか、別途用意したメソッド内で処理を完結させる方法で実現出来ます。
外部クラスから下記のように直接privateフィールドにアクセスしようとした場合はエラーとなります。
「フィールド Sample.text1 は不可視です」のエラーとなりコンパイルが出来ません。

本記事では、Javaのアクセス修飾子の1つである「private」の使い方についてご紹介していきました。
予期せぬエラーやセキュリティ上の問題を起こさせないためにも、アクセス範囲を最小限に限定することは大切です。
データの修正が簡単だからとpublic修飾子ばかり使うのではなく、今回ご紹介したようなprivateやprotectも利用して、適切なデータ範囲を定義するよう意識しておきましょう。

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