Adapter

interface PaymentApi{ //Iterface for payments apis 
    boolean startTransaction(int transactionId);
    boolean checkCompletion(int transactionId);
}

//---------------------
//Make individual adapters to connect 
class PayUAdapter implements PaymentApi{ //Adapter to connect
    PayUApi api = new PayUApi();
    
    public boolean startTransaction(int transactionId){
        System.out.println("Transaction started using PayU "+transactionId);
        return api.start(transactionId);
    }
    
    public boolean checkCompletion(int transactionId){
        System.out.println("Completion status of PayU "+transactionId);
        return api.getStatus(transactionId);
    }
}

class PaytmAdapter implements PaymentApi{ //Adapter to connect
    PaytmApi api = new PaytmApi();
    
    public boolean startTransaction(int transactionId){
        System.out.println("Transaction started using PayTm "+transactionId);
        return api.begin(transactionId);
    }
    
    public boolean checkCompletion(int transactionId){
        System.out.println("Completion status of PayTm "+transactionId);
        return api.checkStatus(transactionId);
    }
}
//------------------------
//These are the APIs provided by Payment Company which have there own methods
class PayUApi{ 
    public boolean start(int id){
        //api runs business logic
        return true;
    }
    public boolean getStatus(int id){
        //api runs business logic
        return true;
    }    
}

class PaytmApi{
    public boolean begin(int id){
        //api runs business logic
        return true;
    }
    public boolean checkStatus(int id){
        //api runs business logic
        return true;
    }    
}

//------------------------

public class Flipkart{
    static PaymentApi api; //initialize with payment api to use
    public Flipkart(){
        api = new PaytmAdapter();
    }
    public static void main(String[] args){
        Flipkart flipkart = new Flipkart(); //make object of flipkart
        api.startTransaction(1); //common functions using adapter class
        api.checkCompletion(1);        
    }
}