Question

1. Using the Comparable Interface

1. Write a class Compare3 that provides a static method largest. Method largest should take three Comparable parameters and return the largest of the three (so its return type will also be Comparable). Recall that method compareTo is part of the Comparable interface, so largest can use the compareTo method of its parameters to compare them.

2. Write a class Comparisons whose main method tests your largest method above.

• First prompt the user for and read in three strings, use your largest method to find the largest of the three strings, and print it out. (It’s easiest to put the call to largest directly in the call to println.) Note that since largest is a static method, you will call it through its class name, e.g., Compare3.largest(val1, val2, val3).

• Add code to also prompt the user for three integers and try to use your largest method to find the largest of the three integers. Does this work? If it does, it’s thanks to autoboxing, which is Java 1.5’s automatic conversion of ints to Integers. You may have to use the -source 1.5 compiler option for this to work.

Answer 1

import java.util.Scanner;

class Comparisons {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.print("Enter first string: ");
        String s1 = in.nextLine();
        System.out.print("Enter second string: ");
        String s2 = in.nextLine();
        System.out.print("Enter third string: ");
        String s3 = in.nextLine();
        System.out.println("Largest string is " + Compare3.largest(s1, s2, s3));
        System.out.print("Enter first integer: ");
        Integer n1 = in.nextInt();
        System.out.print("Enter second integer: ");
        Integer n2 = in.nextInt();
        System.out.print("Enter third integer: ");
        Integer n3 = in.nextInt();
        System.out.println("Largest integer is " + Compare3.largest(n1, n2, n3));
    }
}

class Compare3 {

    public static <T extends Comparable<T>> T largest(T t1, T t2, T t3) {
        T largest = t1;
        if(t2.compareTo(largest) > 0) {
            largest = t2;
        }
        if(t3.compareTo(largest) > 0) {
            largest = t3;
        }
        return largest;
    }
}