Question

Task 1:

1. Write a generic class named MyList, with a type parameter T. The type parameter T should be constrained to an upper bound: the Number class. The class should have as a field an ArrayList of type T. Write the class constructor to create the ArrayList.

2. Write a public method named add, which accepts a parameter of type T. When an argument is passed to the method, add it to the ArrayList.

3. Write a public method display to display all items in the list for testing purpose. Test your class with an instance of type Integers and one of type Double.

4. Write two other methods, largest and smallest, which return the largest and smallest values in the ArrayList.

5. Test the class and its three methods in a program that creates one instance of MyList to store Integers. Demo your program for credit.

Task 2:

1. Modify the MyList class that you wrote in Task 1 so the type parameter T should accept any type that implements the Comparable interface.

2. Test the class in a program that creates one instance of MyList to store Integers, another instance to store Strings, and one instance to store objects of a class type that you define separately (e.g. Employee or Customer etc). Demo your program for credit.

Answer 1

import java.util.ArrayList;

public class MyList<T extends Number> {

ArrayList<T> mylist;

MyList() {

mylist = new ArrayList<T>();

}

public void add(T t) {

mylist.add(t);

}

public T min() {

T min = mylist.get(0);

for (T i : mylist) {

if (i.doubleValue() < min.doubleValue())

min = i;

}

return min;

}

public T max() {

T max = mylist.get(0);

for (T i : mylist) {

if (i.doubleValue() > max.doubleValue())

max = i;

}

return max;

}

public String toString() {

return mylist.toString();

}

public static void main(String[] args) {

// TODO Auto-generated method stub

MyList<Double> list = new MyList<Double>();

list.add(2.0);

list.add(8.4);

System.out.println(list.toString());

System.out.println(list.max());

System.out.println(list.min());

MyList<Integer> Ilist = new MyList<Integer>();

Ilist.add(2);

Ilist.add(8);

System.out.println(Ilist.toString());

System.out.println(Ilist.max());

System.out.println(Ilist.min());

}

}

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See Image for TASK 1

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2)

import java.util.ArrayList;

public class MyList<T extends Comparable<T>> {

ArrayList<T> mylist;

MyList() {

mylist = new ArrayList<T>();

}

public void add(T t) {

mylist.add(t);

}

public T min() {

T min = mylist.get(0);

for (T i : mylist) {

if (i.compareTo(min) < 0)

min = i;

}

return min;

}

public T max() {

T max = mylist.get(0);

for (T i : mylist) {

if (i.compareTo(max) > 0)

max = i;

}

return max;

}

public String toString() {

return mylist.toString();

}

public static void main(String[] args) {

// TODO Auto-generated method stub

MyList<String> list = new MyList<String>();

list.add("Chegg");

list.add("123");

System.out.println(list.toString());

}

}

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