Question1:

Integer.MAX_VALUE - Integer.MIN_VALUE == -1

Question2:

public class Question2 {
	public static boolean isHarmonic(double[] a)
	{
		for (int i = 1; i < a.length-1; i++) {
			if (!(a[i] == (a[i-1] + a[i+1])/2))
				return false;
		}
		return true;
	}

	public static void main(String[] args) {
		double[] a = new double[args.length];
		for (int i = 0; i < a.length; i++) {
			a[i] = Double.parseDouble(args[i]);
		}
		System.out.println(isHarmonic(a));
	}
}

Question3:

public class Team {
	List people;
	
	public Team() {
		people = new ArrayList();
	}

	public void addPerson(Person person) {
		people.add(person);
	}
	
	public Person getLeader() {
		Person leader = null;
		for (int i = 0; i < people.size(); i++) {
			Person p = (Person) people.get(i);
			if (leader == null || leader.getAge() < p.getAge())
				leader = p;
		}

		return leader;
	}
	
	public Person getVolunteer() {
		int index = Math.random() * people.size();
		return (Person) people.get(index);
	}
	
	void print(PrintStream out) {
		Person leader = getLeader();
		for (int i = 0; i < people.size(); i++) {
			Person p = (Person) people.get(i);
			if (p == leader)
				out.println(p.getName()+" "+"*");
			else
				out.println(p.getName());
		}
	}
}

Question 4:

public class Primes {
	private boolean[] primes;

	public Primes(int n) {
		primes = new boolean[n];
		for (int i = 2; i < n; i++) {
			if (!primes[i]) {
				for (int j = 2*i; j < n; j+=i) {
					primes[j] = true;
				}
			}
		}
	}
	
	public boolean isPrime(int i) {
		return !primes[i];
	}	
}

Question 5:

public HashMap wordCounts(Scanner in) {
	HashMap map = new HashMap();
	while (in.hasNext()) {
		String word = in.next();
		Object o = map.get(word);
		if (o == null)
			map.put(word,1);
		else
			map.put(word,((int) o)+1);
	}
	return map;
}