Builder Pattern Java

This creates an immutable object which can only be created via a builder object. This is nicer than put everything into a constructor.

```java public class Rocket { private final int height; private final int maxSpeed; private final List cargo;

public static class Builder {
    // Required parameters
    private final int height;
    private final int maxSpeed;

    // Optional parameters - initialized to default values
    private List<Cargo> cargo = new ArrayList<Cargo>();
   
    public Builder(int height, int maxSpeed) {
        this.height = height;
        this.maxSpeed = maxSpeed;
    }

    public Builder withCargo(List<Cargo> cargo) { 
        this.cargo = cargo;
        return this; 
    }

    public Rocket build() {
        return new Rocket(this);
    }
}

private Rocket(Builder builder) {
    height = builder.height;
    maxSpeed = builder.maxSpeed;
    cargo = builder.cargo;
} }