Here is the code we wrote today (5th period, but both classes were similar):

public class Train {
     private int numLocos;
     private int numCars;
     
     public Train() {
         numLocos = 1;
         numCars = 0;
     }
     
     public void increaseSize(int newCars) {
         numCars += newCars;
         numLocos += (newCars / 5);  
     }
     
     public double speed() {
         return 20 - (double)numCars / numLocos;
     }
}

public class VacuumCleaner {
  
    private boolean charged;   //whether vacuum is charged
    private int amountOfDirt;  //how much dirt is in the vacuum
    private int dirtCapacity;  //how much it can hold
    
    public VacuumCleaner(int dirtCap) {
        charged = true;
        amountOfDirt = 0;
        dirtCapacity = dirtCap;
    }
    
    public int use(int availDirt) {
        if(!charged)
          return 0;
          
        int amt = Math.min(availDirt, dirtCapacity-amountOfDirt);
        amountOfDirt += amt;
        charged = false;
        return amt;
    }
    
    public void charge() {
        charged = true;
    }
    
    public int empty() {
        int temp = amountOfDirt;
        amountOfDirt = 0;
        return temp;    
    }
}