MultPractice.java

public class MultPractice implements StudyPractice {
    
    private int numOne;
    private int numTwo;
    
    public MultPractice(int a, int b) {
        numOne = a;
        numTwo = b;
    }
    
    public String getProblem() {
        return numOne + " TIMES " + numTwo;
    }
    
    public void nextProblem() {
        numTwo++; 
    }
    
}

StudyPractice.java

public interface StudyPractice {
    
    /** Returns the current practice problem */
    String getProblem();
  
    /** Changes to the next practice problem */
    void nextProblem();
}