Question

JAVA

Answer the following questions as briefly (but completely) as possible:

1. How do you simplify the max method in the following, using the conditional operator?

    1:     /** Return the max of two numbers */
    2:     public static int max ( int num1, int num2 ) {
    3:         int result;
    4: 
    5:         if ( num1 > num2 )
    6:             result = num1;
    7:         else
    8:             result = num2;
    9:         return result;
   10:     }

2. Write method headers (just the declaration, not the bodies) for the following methods:
   1. Compute a sales commission, given the sales amount and the commission rate.
   2. Display the calendar for a month, given the month and year.
   3. Compute a square root of a number.
   4. Test whether a number is even, and returning true if it is.
   5. Display a message a specified number of times.
   6. Compute the monthly payment, given the loan amount, number of years, and annual interest rate.
   7. Find the corresponding uppercase letter, given a lowercase letter.
3. Identify and correct the errors in the following program:

    1: public class Test {
    2:     public static method1(int n, m) {
    3:         n += m;
    4:         method2 (3. 4);
    5:     }
    6: 
    7:     public static int method2(int n) {
    8:         if ( n > 0 ) return 1;
    9:         else if (n == 0) return 0;
   10:         else if (n < 0) return -1;
   11:     }
   12: }

4. What is pass-by-value? Show the results of the following two programs.

   1.  1: public class Test {
       2:     public static void main ( String [] args ) {
       3:         int max = 0;
       4:         max(1, 2, max);
       5:         System.out.println(max);
       6:     }
       7: 
       8:     public static void max ( int value1, int value2, int max ) {
       9:         if ( value1 > value2 )
      10:             max = value1;
      11:         else
      12:             max = value2;
      13:     }
      14: }

   2.  1: public class Test {
       2:     public static void main ( String [] args ) {
       3:         int i = 1;
       4:         while ( i <= 6 ) {
       5:             method1( i, 2 );
       6:             i++;
       7:         }
       8:     }
       9: 
      10:     public static void method1 ( int i, int num ) {
      11:         for ( int j = 1; j <= i; j++ ) {
      12:             System.out.print( num + " " );
      13:             num *= 2;
      14:         }
      15:         System.out.println();
      16:     }
      17: }

5. What is wrong with the following class?

   1: public class Test {
   2:     public static void method ( int x ) {
   3:     }
   4:     public static int method ( int y ) {
   5:         return y;
   6:     }
   7: }

6. 1. Write an expression that obtains a random integer between 34 and 55, inclusive.
   2. Write an expression that obtains a random integer between 0 and 999, inclusive.
   3. Write an expression that obtains a random number between 5.5 (inclusive) and 55.5 (exclusive).
   4. Write an expression that obtains a random lowercase (English) letter.
7. How many times is the factorial method in the following invoked, for the call factorial(6)?

    1: import java.util.Scanner;
    2: 
    3: public class ComputeFactorial {
    4:     public static void main ( String [] args ) {
    5:         Scanner input = new Scanner( System.in );
    6:         System.out.print( "Enter a nonnegative integer: " );
    7:         int n = input.nextInt();
    8: 
    9:         // Display factorial
   10:         System.out.println( "Factorial of " + n + " is " + factorial(n) );
   11:     }
   12: 
   13:     /** Return the factorial for the specified number */
   14:     public static long factorial ( int n ) {
   15:         if ( n == 0 ) // Base case
   16:             return 1;
   17:         else
   18:             return n * factorial( n - 1 ); // Recursive call
   19:     }
   20: }

8. Suppose that the class F is defined as shown below. Let f be an instance of F. Which of the following statements are syntactically correct?

   1: public class F {
   2:   int i;
   3:   static String s;
   4:   void iMethod () {
   5:   }
   6:   static void sMethod () {
   7:   }
   8: }

   1. System.out.println(f.i);
   2. System.out.println(f.s);
   3. f.iMethod();
   4. f.sMethod();
   5. System.out.println(F.i);
   6. System.out.println(F.s);
   7. F.iMethod();
   8. F.sMethod();
9. Add the static keyword in the place of ?, if appropriate, in the code below.

    1: public class Test {
    2:     private int count;
    3:     public ? void main ( String [] args ) {
    4:         ...
    5:     }
    6:     public ? int getCount () {
    7:         return count;
    8: }
    9: public ? int factorial ( int n ) {
   10:     int result = 1;
   11:     for ( int i = 1; i <= n; i++ )
   12:         result *= i;
   13:     return result;
   14: }
   15: }

10. Can each of the following statements be compiled?
    1. Integer i = new Integer("23");
    2. Integer i = new Integer(23);
    3. Integer i = Integer.valueOf("23");
    4. Integer i = Integer.parseInt("23", 8);
    5. Double d = new Double();
    6. Double d = Double.valueOf("23.45");
    7. int i = (Integer.valueOf("23")).intValue();
    8. double d = (Double.valueOf("23.4")).doubleValue();
    9. int i = (Double.valueOf("23.4")).intValue();
    10. String s = (Double.valueOf("23.4")).toString();
11. 1. How do you convert an integer into a string?
    2. How do you convert a numeric string into an integer?
    3. How do you convert a double number into a string?
    4. How do you convert a numeric string into a double value?

Answer 1

Max method using conditional operators:

Conditional operator is a ternary operator where it checks the condition before question mark. If the condition is true it will set the result value as num1, else it will set the value of result as num2.

public static int max(int num1,int num2){

       int result = (num1>num2)?num1:num2;

       return result

}

Method headers:

1. public double computeSalesCommision(double amount,double commission_rate){

    }

2. public void displayCalender(String month,int year){

    }

3. public double squareRoot(int num){

   }

4. public Boolean isEven(int num){

   }

5. public displayMsg(String msg, int n){

   }

6. public double monthlyPayment(double loan_amount, int no_of_years,double rates){

   }

7. public char correspondingUpperCase(char c){

   }

Errors in the code:

1. In this program, the method declaration itself is incorrect. Datatype is required before parameter m and the return type is not mentioned in the declaration. On line 4, the argument passed to method2 is in incorrect format as there is space between 3 and 4 which is not required.

The correct code is:

 public class Test {
     public static void method1(int n, int m) {
         n += m;
         method2 (3.4);
     }
 
     public static int method2(int n) {
         if ( n > 0 ) return 1;
         else if (n == 0) return 0;
         else if (n < 0) return -1;
     }
}

Pass-by-Value:

In pass-by-value there is two independent variable swith same value i.e the caller and callee both have different variables with same value. The changes made to the parameter by the callee will not affect the value of actual variable in the caller method.

Results:

1. Answer: 0

Here the pass-by-value concept is used where the changes made by the max() method will not affect the value of max variable.

2. Answer:

       2

   2 4 
   2 4 8 
   2 4 8 16 
   2 4 8 16 32 
   2 4 8 16 32 64 
Here the next number is the multiplication of the current number and 2. This loop iterates for 6 times.

In the class Test both the method has a same signature for method(). When we call the method(), Java compiler will get confused as there is two method with same signature. This can be solved using overloading or overriding concept.