Question 1

Question 1What is a function ? What is its other name ? What is function prototype ?

Accepted Answer

A function is a named block of code within a class. It executes a defined set of instructions when called from another part of the program.A function is also known as a member method.A method/function prototype is the first line of the function definition that contains the access specifier, return type, method name and a list of parameters.

Question 2

Question 2What are actual and formal parameters of a function ?

Accepted Answer

The parameters that appear in the method call statement are called actual parameters.The parameters that appear in the method definition are called formal parameters.For example,class ParameterDemo  
{
    double square(double x)    {
        return Math.pow(x,2);
    }
    
    public static void main(String args[])
    {
        ParameterDemo obj = new ParameterDemo();
        double n = 5.3;
        double sq = obj.square(n);
    }
}Here, x is the formal parameter and n is the actual parameter.

Question 3

Question 3How do you define and invoke a method?

Accepted Answer

The syntax of a method definition is:[access-modifier] type method-name (parameter-list){    method-body;}To invoke a method, write the name of the method and specify the value of arguments of its parameter list. Below example shows the definition and invocation of a method:public class DisplayMessageDemo {

public void DisplayMessage() {
        System.out.println("Hello World!");
    }

public void MyMessage() {
        DisplayMessage();
    }
}

Question 4

Question 4A function argument is a value returned by the function to the calling program. (T/F) ?

Accepted Answer

False.Reason — A function argument is the value passed to the function by the method call statement at the time of method call. The value returned by the function is called the return value of the function.

Question 5

Question 5How many values can be returned from a function ?

Accepted Answer

A function can return only one value because as soon as return statement is executed, the execution of the method terminates and control is transferred to the method call statement.

Question 6

Question 6Explain the difference between actual and formal parameters.

Accepted Answer

The parameters that appear in the method definition are called formal or dummy parameters whereas the parameters that appear in the method call are called actual parameters.

Question 7

Question 7When a function returns a value, the entire function call can be assigned to a variable. (T/F) ?

Accepted Answer

TrueExample —class Demo
{
    int sum(int a, int b)   {
        int sum = a + b;
        return sum;
    }

public static void main(String args[])  {
        Demo obj = new Demo();
        int ans = obj.sum(10, 20);
        System.out.println(ans);
    }
}

Question 8

Question 8(a)Identify the errors in the function skeletors given below :float average (a, b) { }

Accepted Answer

The data type of arguments a and b is not specified.The prototype of the function must specify the data type of the formal parameters. The correct statement is as follows:float average (float a, float b) { }

Question 9

Question 8(b)Identify the errors in the function skeletors given below :float mult (int x, y) { }

Accepted Answer

The data type of argument y is not specified.The prototype of the function must specify the data type of the formal parameters. The correct statement is as follows:float mult (int x, int y) { }

Question 10

Question 10What is an ambiguous invocation? Give an example.

Accepted Answer

Sometimes there are two or more possible matches in the invocation of an overloaded method. In such cases, the compiler cannot determine the most specific match. This is referred to as ambiguous invocation. It causes a compile time error. For example, the below program will cause a compile time error due to ambiguous invocation:public class AmbiguousDemo {

public static double max(double num1, int num2) {
        if (num1 > num2)
            return num1;
        else
            return num2;
    }

public static double max(int num1, double num2) {
        if (num1 > num2)
            return num1;
        else
            return num2;
    }

public static void main(String args[]) {
        /*
         * This line will cause a compile time error
         * as reference to max is ambiguous
         */
        System.out.println(max(19, 20));
    }
}

Question 11

Question 9Given the method below, write a main() method that includes everything necessary to call given method.int thrice (int x)
{
return x * 3 ;
}

Accepted Answer

public class Methodcall
{
    int thrice (int x)
    {
        return x * 3 ;
    }
    
    public static void main(String args[])
    {
		Methodcall obj = new Methodcall();
        int ans;
        ans = obj.thrice(5);	
    }
}

Question 12

Question 10What is the principal reason for passing arguments by value ?

Accepted Answer

The principal reason for passing arguments by value is that the actual parameters that are used to call the method cannot be modified by the called method because any changes that occurs inside the method is on the method's copy of the argument value. The original copy of the arguments remains intact.

Question 13

Question 11When an argument is passed by reference,a variable is created in the function to hold the argument's value.the function cannot access the argument's value.a temporary variable is created in the calling program to hold the argument's value.the function accesses the argument's original value in the calling program.

Accepted Answer

the function accesses the argument's original value in the calling program.Reason — In call by reference, the called method does not create its own copy of original values, rather, it refers to the original values through the references. Thus, the called method works with the original data and any change in the values gets reflected to the data.

Question 14

Question 14A palindromic prime is a prime number and also palindromic. For example, 131, 313, and 757 are prime numbers and also palindromic prime numbers. Write a program that displays the first 100 palindromic prime numbers.

Accepted Answer

public class KboatPalindromicPrime
{
    public static boolean isPrime(int n) {
        int c = 0;
        for (int i = 1; i <= n; i++) {
            if (n % i == 0) {
                c++;
            }
        }
        
        boolean prime = c == 2;
        return prime;
    }

public static boolean isPalindrome(int n) {
        int num = n, revNum = 0;
        while (num != 0) {
            int digit = num % 10;
            num /= 10;
            revNum = revNum * 10 + digit;
        }

boolean palin = revNum == n;
        return palin;
    }

public static void main(String args[]) {
        int x = 1, count = 0;
        while (count < 100) {
            if (isPrime(x) && isPalindrome(x)) {
                count++;
                System.out.println(x);
            }
            x++;
        }
    }
}Output

Question 15

Question 15Differentiate between the following:Call by value and Call by reference

Accepted Answer

Call by valueCall by referenceValues of actual parameters are copied to formal parameters.Reference of actual parameters is passed to formal parameters.Changes made to formal parameters are not reflected back to actual parameters.Changes made to formal parameters are reflected back to actual parameters.Pure and Impure methodsPure methodsImpure methodsPure methods take objects and/or primitive data types as arguments but does not modify the objects.Impure methods change the state of received objects.Pure methods doesn't have side effects.Impure methods have side effects.Simple Method and Overloaded methodSimple MethodOverloaded methodSimple Methods have unique names.In case of Overloaded methods, there are two or more methods with the same name.We can identify the method being invoked by looking at its name.We need to examine the method's number and type of parameters to determine which method will be invoked.

Question 16

Question 14What are the three types of functions in Java?

Accepted Answer

The three types of functions in Java are-Computational methods — The methods that calculate or compute some value and return the computed value. Computational methods always return a computed result. For example, Math.sqrt( ) and Math.cos( ).Manipulative methods — The methods that manipulate information and return a success or failure code. Generally, if value 0 is returned, it denotes successful operation; any other number denotes failure.Procedural methods — The methods that perform an action and have no explicit return value. For instance, System.out.println() method is a procedural method.

Question 17

Question 15Write a function that interchanges the value of two integers A and B without using any extra variable.

Accepted Answer

void swap(int a, int b)   {
    a = a + b;
    b = a - b;
    a = a - b;
}

Question 18

Question 16Give the prototype of a function check which receives a character ch and an integer n and returns true or false.

Accepted Answer

boolean check(char ch, int n)

Question 19

Question 17Write a function that takes an int argument and doubles it. The function does not return a value.

Accepted Answer

void doubleNum(int n)   {
    n = n + n;
}

Question 20

Question 18Differentiate between CALL by reference and CALL by value.

Accepted Answer

Call by valueCall by referenceActual parameters are copied to formal parameters.Formal parameters refer to actual parameters.Any changes to formal parameters are not reflected onto the actual parameters.The changes to formal parameters are reflected onto the actual parameters.All primitive data types are passed using Call by value.All reference data types like arrays and objects of classes are passed using Call by reference.It is used to keep original data secure and unchanged.It is used when the original data values need to be modified.

User-Defined Methods