SOFT2201/COMP9201 Week 2 Tutorial

swap (a ,  b);

System .out .println (a);

System .out .println (b);

}

}

Based on the above program, we are now changing the variables into an array as follows. What will be your answer to the above same questions?

public class Program {

public static void swap (int []  array)  {

int temp  =  array [ 0 ];

array [ 0 ]  =  array [ 1 ];

array [ 1 ]  =  temp;

}

public static void main (String []  args)  {

int []  arr  =  {50 , 100 };

swap (arr);

System .out .println (arr [ 0 ]);

System .out .println (arr [ 1 ]);

}

}

Question 1: Reverse

Write a function that reverses an integer array.

We would encourage you write a reverse function that is in place. By this we mean that you do not copy the contents into another array and only use the array given.

public class Reverse {

public static void reverse (int array [])  {

//Your  code  here,  must  perform  an  inplace  reverse

}

}

Example

//If  you  have  an  array  that  is:

{  1,  2,  3,  4,  5,  6,  7,  8  }

//Output

{  8,  7,  6,  5,  4,  3,  2,  1  }

Question 2: Comparing and sorting

Implement a program that will sort a collection of Strings in reverse order. Do not reverse the list but create a Comparator to order the collection.

import java .util .List ;

import java .util .Collections ;

public class App {

public static void main (String []  args)  {

List  strings  =  Arrays .asList (new String []  {

"One" ,

"Two" ,

"Three" ,

"Four" ,

"Five" ,

"Six" ,

"Seven"

});

Collections .sort (strings ,  / *  Your  comparator  here   */);

for (String  s   :  strings)  {

System .out .println (s);

}

}

}

Your program should output the following:

Two

Three

Six

Seven

One

Four

Five

Question 3: Union

You are tasked with writing a method that will compute the union between two arrays. You will need to detect overlap between the two sets and ensure you are not including an element that appears in both sets more than once.

You have been provided a scaffold for the above problem

public class ArrayUnion {

public static int []  union (int []  a , int []  b)  {

return null;

}

public static void main (String []  args)  {

}

}

You will need to check if there is a duplicate element in both sets as you should only return one element, not both.

Your method must return null if either array is null.

Example 1

int []  x  =  {3 ,  2 ,  7 };

int []  y  =  {3 ,  8 ,  9 };

int []  result  =  union (x ,  y);

//{2,  3,   7,  8,  9},  it  is  not  necessary  to  sort  the  array

Example 2

int []  x  =  {2 ,  2 ,  7 };

int []  y  =  { 1 ,  9 };

int []  result  =  union (x ,  y);

//{1,  2,   7,  9},  it  is  not  necessary  to  sort  the  array

Example 3

int []  x  = null;

int []  y  =  { 6 ,  8 ,  9 };

int []  result  =  union (x ,  y);

//nulldmesg

Inheritance

Classes

Classes are a fundamental construct within java, they allow the programmer to aggregate data and functionality under a defined type. This feature isn’t just for reusability and simplicity, we are able to safely read and write to memory by ensuring we adhere to the type system rules and satisfy the constraints enforced by the compiler.

Within Java, all classes inherit from the Object type, providing a definition for toString and equals which can be overridden.

Interfaces and Abstract Classes

Interfaces within java allow the programmer to create a type specifying abstract methods. When we specify that a class implements an interface, it must ensure a method body for each method specified in the interface.

interface Drivable {

public boolean start ();

public boolean stop ();

public void move ();

}

In the Drivable example, any type that implements this interface must also implement start, stop and move, allowing us to categorise objects of different types under one. Within our applica- tion, types such as Car, Truck and Train can implement the Drivable type.

Similar to an interface, an abstract  class can be used to provide a type association with common properties, however within Java, a class is limited to inheriting from just one class where it can implement many interfaces.

• If our application contained a Car, Truck and Train, would we group these classes using an interface or abstract class?

Question 4: Polymorphism

You have been given the following java code, you may assume that the program compiles successfully.

interface Animal {

void talk ();

}

public class Zoo {

public static void makeNoise (List  animals)  {

for (Animal  a   :  animals)  {

a .talk ();

}

}

public static void outputToString (List