How to write code for Java factory design pattern

Implementation

We will create a Shape interface and concrete classes that implement the Shape interface. A factory class ShapeFactory will be defined in the next step.

FactoryPatternDemo This is a demonstration class that will use ShapeFactory to obtain a Shape object. It will pass the information (CIRCLE/RECTANGLE/SQUARE) to the ShapeFactory to get the required object type.

The structure of implementing the factory pattern is shown in the figure below-

java-61.jpg

step 1

​Create an interface-

Shape.java

publicinterfaceShape{

voiddraw();

}

Step 2

Create a concrete class that implements the same interface. Several categories are shown below-

Rectangle.java

​publicclassRectangleimplementsShape{

@Override

publicvoiddraw(){

System.out.println("InsideRectangle::draw()method.");

}

}

Square.java

​publicclassSquareimplementsShape{

@Override

publicvoiddraw(){

System.out.println("InsideSquare::draw()method.");

}

}

​Circle.java

​publicclassCircleimplementsShape{

@Override

publicvoiddraw(){

System.out.println("InsideCircle::draw()method.");

}

}

Step 3

Create a factory to generate objects of specific classes based on given information.

ShapeFactory.java

​publicclassShapeFactory{

//usegetShapemethodtogetobjectoftypeshape

publicShapegetShape(StringshapeType){

​if(shapeType==null){

returnnull;

}

​if(shapeType.equalsIgnoreCase("CIRCLE")){

returnnewCircle();

}elseif(shapeType.equalsIgnoreCase("RECTANGLE")){

returnnewRectangle();

}elseif(shapeType.equalsIgnoreCase("SQUARE")){

returnnewSquare();

}

returnnull;

}

}

Step 4

Use a factory to obtain an object of a specific class by passing information such as type.

FactoryPatternDemo.java

​publicclassFactoryPatternDemo{

publicstaticvoidmain(String[]args){

ShapeFactoryshapeFactory=newShapeFactory();

//getanobjectofCircleandcallitsdrawmethod.

Shapeshape1=shapeFactory.getShape("CIRCLE");

​ //calldrawmethodofCircle

shape1.draw();

//getanobjectofRectangleandcallitsdrawmethod.

Shapeshape2=shapeFactory.getShape("RECTANGLE");

​ //calldrawmethodofRectangle

shape2.draw();

//getanobjectofSquareandcallitsdrawmethod.

Shapeshape3=shapeFactory.getShape("SQUARE");

//calldrawmethodofcircle

shape3.draw();

}

}

Step 5

The verification output results are as follows-

​InsideCircle::draw()method.

​InsideRectangle::draw()method.

​InsideSquare::draw()method.

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