OOP Example in java | class, method, constructor, getter and setter, access modifiers, throw exception
- برمجة جافا
- 2022-02-14
- softwareEngineer
الأجوبة
Question1:
public class Rectangle {
private final String name;
private double side1;
private double side2;
private double side3;
private double side4;
private static int noRectangles;
// full-argument constructor
public Rectangle(String name, double side1, double side2, double side3, double side4) {
if (name == null) {
this.name = "InternalName" + noRectangles;
} else {
this.name = name;
}
if (side1 <= 0) {
this.side1 = 1;
} else {
this.side1 = side1;
}
if (side2 <= 0) {
this.side2 = 1;
} else {
this.side2 = side2;
}
if (side3 <= 0) {
this.side3 = 1;
} else {
this.side3 = side3;
}
if (side4 <= 0) {
this.side4 = 1;
} else {
this.side4 = side4;
}
if (side1 != side3 || side2 != side4) {
throw new IllegalArgumentException("Not a rectangle!");
}
noRectangles++;
}
// no-argument constructor
public Rectangle() {
this("InternalName" + noRectangles, 1.0, 1.0, 1.0, 1.0);
}
// copy constructor
public Rectangle(Rectangle r) {
this(r.name, r.side1, r.side2, r.side3, r.side4);
}
// getters
public String getName() {
return name;
}
public double getSide1() {
return side1;
}
public double getSide2() {
return side2;
}
public double getSide3() {
return side3;
}
public double getSide4() {
return side4;
}
public static int getNoRectangles() {
return noRectangles;
}
// setters
public void setSide1(double side1) {
if (side1 <= 0) {
this.side1 = 1;
} else {
this.side1 = side1;
}
}
public void setSide2(double side2) {
if (side2 <= 0) {
this.side2 = 1;
} else {
this.side2 = side2;
}
}
public void setSide3(double side3) {
if (side3 <= 0) {
this.side3 = 1;
} else {
this.side3 = side3;
}
}
public void setSide4(double side4) {
if (side4 <= 0) {
this.side4 = 1;
} else {
this.side4 = side4;
}
}
public double computeArea() {
return this.side1 * this.side2;
}
public double computeArea(String unit) {
if (unit.equalsIgnoreCase("cm")) {
// return this.side1 * this.side2 * 10000;
return this.computeArea() * 10000;
/*another way:*/
// return this.computeArea() * Math.pow(100, 2);
/*another way also:*/
//return (this.side1*100)*(this.side2*100);
} else if (unit.equalsIgnoreCase("inch")) {
return this.computeArea() * Math.pow(39.37, 2);
/*another way:*/
//return (this.side1*39.37)*(this.side2*39.37);
} else {
throw new IllegalArgumentException("Invalid unit!");
}
}
public double computePerimeter() {
return (this.side1 + this.side2) * 2;
}
public double computePerimeter(String unit) {
if (unit.equalsIgnoreCase("cm")) {
//return this.computePerimeter() * 100;
/*another way:*/
return ((this.side1*100)+(this.side2*100))*2;
} else if (unit.equalsIgnoreCase("inch")) {
//return this.computePerimeter() * 39.37;
/*another way:*/
return ((this.side1*39.37)+(this.side2*39.37))*2;
} else {
throw new IllegalArgumentException("Invalid unit!");
}
}
}
Question2:
import java.util.Scanner;
import java.text.DecimalFormat;
public class PractisingClasses {
/**
*
* This method extends the given array by creating another array whose
* size is greater than the size of the given array by 1. It copies the
* elements of the given array to the new array.
*
* @param recArry an array to extend
* @return Rectangle[]: the new array.
*/
public static Rectangle[] extendRecArray(Rectangle[] recArr) {
// Create a new array that has one more space than recArr
Rectangle[] newRecArr = new Rectangle[recArr.length + 1];
// Copy the elements of recArr to the new Array
for (int i = 0; i < recArr.length; i++) {
newRecArr[i] = recArr[i];
}
// return the new Array
return newRecArr;
}
/**
*
* This method checks if there is a rectangle in the array 'rec' whose name
* is 'name'.
*
* @param rec an array rectangles.
* @param name a name to check if there is any rectangle having its name as it.
* @return Rectangle[]: the new array.
*/
public static boolean nameExists(Rectangle[] rec, String name) {
boolean exists = false;
for (int i=0; i < rec.length && !exists; i++) {
if (rec[i].getName().equalsIgnoreCase(name)) {
exists = true;
}
}
return exists;
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
// TODO code application logic here
Scanner sc = new Scanner(System.in);
int userIn = 0;
Rectangle[] recList = new Rectangle[0];
do {
System.out.println("Please choose one of the following options:");
System.out.println("\t1. Create a default rectange.");
System.out.println("\t2. Create a defined rectangle.");
System.out.println("\t3. Exit.");
System.out.print("Enter your choice: ");
userIn = sc.nextInt();
switch(userIn) {
case 1:
// extend the array recList by one (check this method above).
recList = extendRecArray(recList);
recList[recList.length - 1] = new Rectangle();
break;
case 2:
String name = null;
do {
System.out.print("Enter name: ");
name = sc.next();
if (name.startsWith("InternalName") ||
nameExists(recList, name)) {
System.out.println("ERROR: Name exists or starts with "
+ "\'InternalName\'");
}
} while (name.startsWith("InternalName") ||
nameExists(recList, name));
System.out.print("Enter the length of the first side in meters: ");
double first = sc.nextDouble();
System.out.print("Enter the length of the second side in meters: ");
double second = sc.nextDouble();
System.out.print("Enter the length of the third side in meters: ");
double third = sc.nextDouble();
System.out.print("Enter the length of the forth side in meters: ");
double fourth = sc.nextDouble();
recList = extendRecArray(recList);
recList[recList.length - 1] = new Rectangle(name, first,
second, third, fourth);
break;
default:
if (userIn != 3) {
System.out.println("ERROR: unknow input!");
}
}
} while(userIn != 3);
double largestArea = Double.MIN_VALUE;
double smallestArea = Double.MAX_VALUE;
Rectangle largestRec = null;
Rectangle smallestRec = null;
// to format the decimal numbers in two decimal points.
DecimalFormat dc = new DecimalFormat("#.##");
for (int i=0; i < recList.length; i++) {
System.out.println("######################################");
System.out.println("Name: " + recList[i].getName());
System.out.println("Area in meter: " +
dc.format(recList[i].computeArea()));
System.out.println("Area in cm: " +
dc.format(recList[i].computeArea("cm")));
System.out.println("Area in inch: " +
dc.format(recList[i].computeArea("inch")));
System.out.println("Perimeter in meter: " +
dc.format(recList[i].computePerimeter()));
System.out.println("Perimeter in cm: " +
dc.format(recList[i].computePerimeter("cm")));
System.out.println("Perimeter in inch: " +
dc.format(recList[i].computePerimeter("inch")));
// find the smallest and largest rectangle
if (recList[i].computeArea() > largestArea) {
largestArea = recList[i].computeArea();
largestRec = recList[i];
}
if (recList[i].computeArea() < smallestArea) {
smallestArea = recList[i].computeArea();
smallestRec = recList[i];
}
}
System.out.println("#############################");
System.out.println("#############################");
System.out.println("Largest rec name: " + largestRec.getName());
System.out.println("Largest rec area: " +
dc.format(largestRec.computeArea()));
System.out.println("#############################");
System.out.println("Smallest rec name: " + smallestRec.getName());
System.out.println("Smallest rec area: " +
dc.format(smallestRec.computeArea()));
// Print the number of Rectangle objects that have been created.
// Note: Calling a static member does not need creating an object.
// You can call it using the class name as below.
System.out.println("#############################");
System.out.println("The number of rectangle objects that have "
+ "been created is: " + Rectangle.getNoRectangles());
}
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