Strategy 4

Write the interface or class in each question.

1. The interface G has methods String who(), int when(), and void walk(int howlong).

2. Copy or type the tester class.

public class TestG {
  public static void tester(G x) {
    System.out.println(x.who());
    System.out.println(x.when());
    x.walk(5);
    System.out.println(x.when());
  }
}

3. The class G1 implements the G interface. Use + to join strings.

public static void demoA() {
    G1 x = new G1("Samuel",10,30);
    tester(x); 
    // Output: "Big Samuel" 1030 1035
}

4. The class G2 implements the G interface. When asked to walk for N minutes, these objects actually take 2N minutes.

public static void demoB() {
    G2 y = new G2("Jordan", 8, 20);
    tester(y);
    // Output: "Little Jordan" 820 830
}

5. The class G2X extends G2. The name changes to add “Fast” but nothing else changes.

public static void demoC() {
    G2 y = new G2X("Jordan", 8, 20);
    tester(y);
    // Output: "Fast Little Jordan" 820 830
}

6. Unrelated to the above, create a class H that counts from its lower limit to its upper limit. Methods: int start(), boolean done(), int next().

   • The start() method gives the first number to count from.
   • The next() method gives the next number in the sequence.
   • The done() method returns true when the count has reached the end number.

Calling demoD() produces output: 31 32 33 34 35 36 37 38 39 40

Below is the demoD and testH method. The demoD method is complicated just to show you how to write a conditional (if statement) in Java.

public static void demoD() {
    H a = new H(30, 40);
    int s = 0; // choose "else" clause always
    if ( s < 0 ) {
        System.out.println("Small s, no work.");
    } else {
        testH(a);
    }
}

public static void testH(H b) {
    int n = b.start();
    while (! b.done()) {
      n = b.next();
      System.out.println(n);
    }
}

7. Make a class H4 extending H, altering the behavior so it counts up by 4. Test your class by modifying the demoD function or by using the short code segment below (put in the same class as your testH).

public static void demoE() { 
    testH(new H4(20,60)); // print 24, 28, ..., 60
}

8. Modify your H class if necessary so that it resets to the beginning every time start() is called.

public static void demoF() { 
    H x = new H(20,30);
    testH(x); // print 21, 22, ..., 30
    testH(x); // print 21, 22, ..., 30 again
}