COMP2511

25T1 Week 10 🥳

Thursday 9am-12pm (H09B)

 

Slides by Sam Zheng (z5418112)

Original slides by Alvin Cherk

MyExperience ->

Admin

  • If you are doing assignment-iii, please make sure you submit it following the instructions in the spec.
    • No autogenerated UMLs
    • No ChatGPT blogs pls
    • Include video that is public. We will not be chasing this up since marking will happen during week 11/12
  • Due next Tuesday 29th without penalty

MyExperience

Please fill it in (5 mins)

Builder Pattern

Builder Pattern

Creational Pattern

  • Allows you to create complex objects step by step
  • Allows you to produce different types and representations of an object using the same construction code

Builder Pattern

public class Car {
    private String engine;
    private int wheels;
    private boolean sunroof;
    private String color;
    private boolean gps;

    public Car(String engine, int wheels, boolean sunroof, String color, boolean gps) {
        this.engine = engine;
        this.wheels = wheels;
        this.sunroof = sunroof;
        this.color = color;
        this.gps = gps;
    }

    @Override
    public String toString() {
        return "Car{" + "engine=" + engine + ", wheels=" + wheels +
               ", sunroof=" + sunroof + ", color=" + color + ", gps=" + gps + '}';
    }
}

// Usage
Car car = new Car("V8", 4, true, null, false);
Car car2 = new Car("I4", 4, false, "red", true);
// Not every car will use every parameter, and this could get very long with more complex objects!

Consider this example:

Builder Pattern

public class Car {
    private String engine, color;
    private int wheels;
    private boolean sunroof, gps;

    private Car(Builder b) {
        this.engine = b.engine;
        this.wheels = b.wheels;
        this.sunroof = b.sunroof;
        this.color = b.color;
        this.gps = b.gps;
    }

    public static class Builder {
        private String engine, color = "white";
        private int wheels = 4;
        private boolean sunroof = false, gps = false;

        public Builder engine(String engine) { this.engine = engine; return this; }
        public Builder sunroof(boolean sunroof) { this.sunroof = sunroof; return this; }
        public Builder color(String color) { this.color = color; return this; }
        public Builder gps(boolean gps) { this.gps = gps; return this; }
        public Car build() { return new Car(this); }
    }
}

// Usage - you don't have to specify all parameters, only call methods you need/want!
Car car = new Car.Builder()
                 .engine("V8")
                 .gps(true)
                 .build();

Code Demo

In our system, we have trains which contain many engines and/or wagons. As in a normal train, these engines/wagons are ordered sequentially from the front of the train to the back.

Engines provide a certain amount of power and wagons require a certain amount of power to pull. At each point along the train, taking into account preceeding engines/wagons, the sum of the engine power must be greater than the sum of the wagon's required power. Otherwise, the rest of the train will be left behind!

There are three types of wagons:

  • Passenger wagons which require 500 engine power each
  • Cargo wagons which require 1000 engine power each
  • Engines which provide power. They can be created at any power. For our system, we will create them with two variants. A "high powered" engine (2,000 power) and a "normal" engine (1,000) power.

Create a train builder that constructs a train in order, wagon by wagon with the above constraint. If the above constraint is violated at any point, throw an IllegalStateException.

Kahoot

Exam Tips

Exam Tips

  • Practice good exam techniques
  • Get familiar with writing Java & Generics
  • Learn the patterns and the differences (YouTube has some really good resources if you don't understand certain ones).
  • Know code smells and methods of refactoring
    • refactoring.guru!
  • Please ensure that your code compiles. Even if you didn't finish the question, at least get it to a compliable state (Write all the placeholder code you need to, to achieve this)
  • Please ensure that you get familiar with VSCode.
  • Open VSCode in the correct folder (for syntax support)
  • Don't waste all your time on 10% of the exam
  • If you get particularly stuck on a question, come back to it later
  • You can use dot points if you're short on time or prefer to
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