Practice questions on Java Classes and Objects

Level 1
Level 2

Level 1

Write a program to print the area of a rectangle by creating a class named 'Area' having two methods. First method named as 'setDim' takes length and breadth of rectangle as parameters and the second method named as 'getArea' returns the area of the rectangle. Length and breadth of rectangle are entered through keyboard.

Create a class named 'Student' with String variable 'name' and integer variable 'roll_no'. Assign the value of roll_no as '2' and that of name as "John" by creating an object of the class Student.

class Student{
  String name;
  int roll_no;
}

class Ans{
  public static void main(String[] args){
    Student s = new Student();
    s.name = "John";
    s.roll_no = 2;
    System.out.println("Name is "+s.name+" and roll number is "+s.roll_no);
  }
}								

Assign and print the roll number, phone number and address of two students having names "Sam" and "John" respectively by creating two objects of class 'Student'.

Write a program to print the area and perimeter of a triangle having sides of 3, 4 and 5 units by creating a class named 'Triangle' without any parameter in its constructor.

class Triangle{
  int a,b,c;
  public double getArea(){
    double s = (a+b+c)/2.0;
    return Math.pow((s*(s-a)*(s-b)*(s-c)),.5);
  }
  public double getPerimeter(){
    return (a+b+c)/2.0;
  }
}

class Ans{
  public static void main(String[] args){
    Triangle t = new Triangle();
    t.a = 2;
    t.b = 5;
    t.c = 6;
    System.out.println(t.getArea());
    System.out.println(t.getPerimeter());
  }
}								

Write a program to print the area and perimeter of a triangle having sides of 3, 4 and 5 units by creating a class named 'Triangle' with constructor having the three sides as its parameters.

Write a program to print the area of two rectangles having sides (4,5) and (5,8) respectively by creating a class named 'Rectangle' with a method named 'Area' which returns the area and length and breadth passed as parameters to its constructor.

class Rectangle{
  int length;
  int breadth;
  public Rectangle(int l, int b){
    length = l;
    breadth = b;
  }
  public int getArea(){
    return length*breadth;
  }
  public int getPerimeter(){
    return 2*(length+breadth);
  }
}

class Ans{
  public static void main(String[] args){
    Rectangle a = new Rectangle(4,5);
    Rectangle b = new Rectangle(5,8);
    System.out.println("Area : "+a.getArea()+" Perimeter is "+a.getPerimeter());
    System.out.println("Area : "+b.getArea()+" Perimeter is "+b.getPerimeter());
  }
}								

Write a program to print the area of a rectangle by creating a class named 'Area' taking the values of its length and breadth as parameters of its constructor and having a method named 'returnArea' which returns the area of the rectangle. Length and breadth of rectangle are entered through keyboard.

import java.util.*;
class Area{
  int length;
  int breadth;
  public Area(int l, int b){
    length = l;
    breadth = b;
  }
  public int getArea(){
    return length*breadth;
  }
}

class Ans{
  public static void main(String[] args){
    Scanner s = new Scanner(System.in);
    int l,b;

    System.out.println("Enter length");
    l = s.nextInt();
    System.out.println("Enter breadth");
    b = s.nextInt();

    Area a = new Area(l,b);
    System.out.println("Area : "+a.getArea());
  }
}									

Print the average of three numbers entered by user by creating a class named 'Average' having a method to calculate and print the average.

Print the sum, difference and product of two complex numbers by creating a class named 'Complex' with separate methods for each operation whose real and imaginary parts are entered by user.

import java.util.*;
class Complex{
  int real;
  int imag;
  public Complex(int r, int i){
    real = r;
    imag = i;
  }

  public static Complex add(Complex a, Complex b){
    return new Complex((a.real+b.real),(a.imag+b.imag));
  }

  public static Complex diff(Complex a, Complex b){
    return new Complex((a.real-b.real),(a.imag-b.imag));
  }

  public static Complex product(Complex a, Complex b){
    return new Complex(((a.real*b.real)-(a.imag*b.imag)),((a.real*b.imag)+(a.imag*b.real)));
  }

  public void printComplex(){
    if(real == 0 && imag!=0){
      System.out.println(imag+"i");
    }
    else if(imag == 0 && real!=0){
      System.out.println(real);
    }
    else{
      System.out.println(real+"+"+imag+"i");
    }
  }

}

class Ans{
  public static void main(String[] args){
    Complex c = new Complex(4,5);
    Complex d = new Complex(9,4);

    Complex e = Complex.add(c,d);
    Complex f = Complex.diff(c,d);
    Complex g = Complex.product(c,d);
    e.printComplex();
    f.printComplex();
    g.printComplex();
  }
}								

10.

Write a program that would print the information (name, year of joining, salary, address) of three employees by creating a class named 'Employee'. The output should be as follows:
Name        Year of joining        Address
Robert            1994                64C- WallsStreat
Sam                2000                68D- WallsStreat
John                1999                26B- WallsStreat

11.

Add two distances in inch-feet by creating a class named 'AddDistance'.

Level 2

Write a program by creating an 'Employee' class having the following methods and print the final salary.
1 - 'getInfo()' which takes the salary, number of hours of work per day of employee as parameter
2 - 'AddSal()' which adds $10 to salary of the employee if it is less than $500.
3 - 'AddWork()' which adds $5 to salary of employee if the number of hours of work per day is more than 6 hours.

Create a class called 'Matrix' containing constructor that initializes the number of rows and number of columns of a new Matrix object. The Matrix class has the following information:
1 - number of rows of matrix
2 - number of columns of matrix
3 - elements of matrix in the form of 2D array

The Matrix class has methods for each of the following:
1 - get the number of rows
2 - get the number of columns
3 - set the elements of the matrix at given position (i,j)
4 - adding two matrices. If the matrices are not addable, "Matrices cannot be added" will be displayed.
5 - multiplying the two matrices

class Matrix{
  int row;
  int column;
  int[][] a;
  public Matrix(int r, int c){
    row = r;
    column = c;
    a = new int[row][column];
  }

  public int getRows(){
    return row;
  }
  public int getColumns(){
    return column;
  }
  public int getElement(int r, int c){
    return a[r][c];
  }
  public void setElement(int r, int c, int element){
    a[r][c] = element;
  }
  public static Matrix add(Matrix x, Matrix y){
    if((x.row == y.row) && (x.column == y.column)){
      Matrix m = new Matrix(x.row,x.column);
      for(int i = 0;i<m.row;i++){
        for(int j = 0;j<m.column;j++){
          m.setElement(i,j,(x.getElement(i,j)+y.getElement(i,j)));
        }
      }
      return m;
    }
    else{
      System.out.println("Matrices can not be added");
      return new Matrix(0,0);
    }

  }

  public static Matrix product(Matrix x, Matrix y){
      Matrix m = new Matrix(x.row,y.column);
      
      for(int j = 0;j<x.row;j++){
        for(int i = 0;i<y.column;i++){
          int sum = 0;
          for(int k = 0;k<x.column;k++){
            sum = sum+(x.getElement(j,k)*y.getElement(k,i));
            
          }
          m.setElement(j,i,sum);
        }
      }

      return m;
    }

  public void printMatrix(){
    System.out.println("Matrix is :");
    for(int i = 0;i<row;i++){
        for(int j = 0;j<column;j++){
          System.out.print(a[i][j]+"\t");
        }
        System.out.println("");
      }
  }
}

class Ans{
  public static void main(String[] args){
    Matrix m = new Matrix(3,3);
    Matrix n = new Matrix(3,3);
    int k = 1;
    for(int i = 0;i<3;i++){
      for(int j = 0;j < 3;j++){
        m.setElement(i,j,k);
        k++;
        n.setElement(i,j,k);
        k++;
      }
    }

    m.printMatrix();
    n.printMatrix();

    Matrix o = Matrix.add(m,n);
    o.printMatrix();

    Matrix p = Matrix.product(m,n);
    p.printMatrix();
  }
}
									

Level 3

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