OilTank.java

public class OilTank {
    int capacity = 5000;
    int contents = 0;

    public int getCapacity() {
        return this.capacity;
    }

    public int getContents() {
        return this.contents;
    }

    private void setCapacity(int capacity) {
        if (capacity > 0) {
            this.capacity = capacity;
        }
    }

    private void setContents(int contents) {
        if (contents >= 0 && contents <= this.capacity) {
            this.contents = contents;
        } else if (contents > this.capacity) {
            this.contents = this.capacity;
        }
    }

    public OilTank() {
        // Initialize using default values
    }

    public OilTank(int capacity) {
        this.setCapacity(capacity);
    }

    public OilTank(int capacity, int contents) {
        this.setCapacity(capacity);
        this.setContents(contents);
    }

    public boolean isFull() {
        if (this.getCapacity() == this.getContents()) {
            return true;
        } else {
            return false;
        }
    }

    public boolean isEmpty() {
        if (this.getContents() == 0) {
            return true;
        } else {
            return false;
        }
    }

    public boolean isZelfde(OilTank other) {
        if (other != null && this.getContents() == other.getContents() && this.getCapacity() == other.getCapacity()) {
            return true;
        } else {
            return false;
        }
    }

    public String toString() {
        return "Capaciteit: " + this.getCapacity() + ", Contents: " + this.getContents();
    }

    public boolean fill() {
        this.setContents(this.capacity);
        return true;
    }

    public boolean fill(int amount){
        boolean result = false;

        if (amount >= 0 && amount <= this.getCapacity() - this.getContents()) {
            this.setContents(this.getContents()+amount);
            result = true;
        } else if (amount > 0 && amount >= this.getCapacity()-this.getContents()) {
            this.setContents(this.getCapacity());
        }

        return result;
    }

    public int extract() {
        int temp = this.getContents();
        this.setContents(0);
        return temp;
    }

    public int extract(int amount) {
        int temp = this.getContents();
        if (amount > 0) {
            if (temp - amount < 0) {
                this.setContents(0);
                return temp;
            } else {
                this.setContents(this.getContents() - amount);
                return amount;
            }
        }
        return -1;
    }

    public void transferFrom(OilTank other) {
        if (other != null) {
            int transfer = other.getContents()-(this.getCapacity()-this.getContents());
            this.setContents(this.getContents()+transfer);
            other.setContents(other.getContents()-transfer);
        }

    }

    public void isRelativelyFullerThan(OilTank other) {
        if (other != null) {
            float a = this.getContents() / this.getCapacity();
            float b = other.getContents() / other.getCapacity();

            if (a < b) {
                System.out.println("De eerste olietank is voller dan de tweede.");
            } else if (a > b) {
                System.out.println("De tweede olietank is voller dan de eerste.");
            } else {
                System.out.println("De twee olietanken zijn relatief gelijk aan elkaar.");
            }
        }
    }
}