Visitor Design Pattern

Collections contain objects of different types and in those cases some operations have to be performed on all the collection elements without knowing the type
–Checking for instance type is not elegant
Visitor pattern represents an operation to be performed on the elements of an object structure

Class diagram for Visitor Design Pattern

Visitor

Defines a new operation to a class without change

Example Java Code for Visitor Design Pattern 😊

This is the scenario where Doctor visits school and test every child in the school . Its like going through every objects and perform an operation.

Visitor.java

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public interface Visitor {
    public void visit(Visitable visitable);
}

Doctor.java

public class Doctor implements Visitor {

    private String name;

    public Doctor(String name) {
        this.name = name;
    }

    @Override
    public void visit(Visitable visitable) {
        Kid child = (Kid) visitable;
        child.setHealthStatus("bad");
        System.out.println("Child Specialist visited " + child.getName() + " set the status to: " + child.getHealthStatus());

    }

}

Visitable.java

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public interface Visitable {
    public void accept (Visitor visitor);
}

Kid.java

public class Kid implements Visitable {

    private String name;
    private String healthStatus;

    public Kid(String name, String healthStatus) {
        super();
        this.name = name;
        this.healthStatus = healthStatus;
    }

    public void accept(Visitor visitor) {
        visitor.visit(this);
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setHealthStatus(String healthStatus) {
        this.healthStatus = healthStatus;
    }

    public String getHealthStatus() {
        return healthStatus;
    }

}

School.java

public class School {
    static ArrayList<Kid> childlist;
    
    public static void doHealthChckup(Visitor visitor){
        
        for (Kid child:childlist){
            child.accept(visitor);
        }
    
    }
}

Client.java

public class Demo {
    public static void main(String[] args) {
        Kid ram =new Kid("Ram","Good");
        Kid ramesh =new Kid("Ramesh","Good");
        Kid ramu =new Kid("Ramu","Good");
        Kid ramar =new Kid("Ramar","Good");
        Kid ramei =new Kid("Ramie","Good");
        School.childlist=new ArrayList<>();
        School.childlist.add(ram);
        School.childlist.add(ramu);
        School.childlist.add(ramei);
        School.childlist.add(ramu);
        Visitor kadavul =new Doctor("kadavul");
        School.doHealthChckup(kadavul);
        
    }
}

Visitor Design Pattern

Class diagram for Visitor Design Pattern

Visitor

Example Java Code for Visitor Design Pattern 😊

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