Java Beginners Excercises

Que 1: Answer the below questions based on the following Java program:

public class MyFirstProgram {
    public static void main(String[] args){
        System.out.println("hello world");
    }
}

A; What would be the Java file name for the above Java program and why?

Ans: The file name will be MyFirstProgram.java. The file name should be the same as the name of the public class defined.

B: What is the command used to compile and run the above Java program. Write the full command.

Ans: Compile: javac MyFirstProgram.java, Run: java MyFirstProgram

Que 2: How many data types are available in Java?

Ans:

Integer: int, short, long, byte

Floating point: float, double

Char type: char

Boolean type: boolean

Que 3: How can we define variables in Java? Please provide an example.

Ans:

public class DefineSomeVariables

{

    double salary;

   int vacationDays = 12;

   long earthPopulation

   boolean done;

}

Que 4: How can we define constants in Java? Please provide an example.

Ans: We use the keyword final to denote a constant.

public class Constants

{

     public static void main(String[] args)

    {

         final double CM_PER_INCH = 2.54;

         final INCH = 12;

     }

}

Que 5: Which In-built class does Java provide for mathematical operations. Please provide some basic examples using that class.

Ans: Java provide Math class.

Below are some examples:

1: To take the square root of a number, use the sqrt method:

double x = 4;

double y = Math.sqrt(x);

System.out.println(y); // prints 2.0

2: The Math class supplies the usual trigonometric functions:

Math.sin

Math.cos

Math.tan

Math.atan

Math.atan2

Que 6: What is the data type conversion in Java? Please explain using an example.

Ans: When we assign the value of one data type to another, the two types might not be compatible with each other. If the data types are compatible, then Java will perform the conversion automatically known as Automatic Type Conversion and if not then they need to be cast or converted explicitly.

For example:

The syntax for casting is to give the target type in parentheses, followed by the variable name.

double x = 9.997;

int nx = (int) x;

Now, the variable nx has the value 9 because casting a floating-point value to an integer discards the fractional part.

Que 7: Explain operator combining in Java using an example.

Ans:

x += 4;

is equivalent to

x = x + 4;

(In general, place the operator to the left of the = sign, such as *= or %= .)

If the operator yields a value whose type is different than that of the left-

hand side, then it is coerced to fit. For example, if x is an int , then the statement

x += 3.5;

is valid, setting x to (int)(x + 3.5) .

Que 8: Is Java supports Increment and Decrement Operators? If yes then explain using an example.

Ans: Yes java supports both Increment and Decrement Operators.

Example:

int n = 12;

n++;

changes n to 13. Since these operators change the value of a variable, they cannot

be applied to numbers themselves. For example, 4++ is not a legal statement.

int a = 2 * ++m; // now a is 16, m is 8

int b = 2 * n++; // now b is 14, n is 8

The same way we can do --n and n--.

Que 9: What are the relational operators in Java? Provide some examples.

Ans: Java has six relational operators that compare two numbers and return a boolean value. The relational operators are <, >, <=, >=, ==, and !=.

Examples:

x < y	Less than	True if x is less than y, otherwise false.
x > y	Greater than	True if x is greater than y, otherwise false.
x <= y	Less than or equal to	True if x is less than or equal to y, otherwise false.
x >= y	Greater than or equal to	True if x is greater than or equal to y, otherwise false.
x == y	Equal	True if x equals y, otherwise false.
x != y	Not Equal	True if x is not equal to y, otherwise false.

Que 10: What are Enumerated types in Java? Explain using an example.

Ans: Sometimes, a variable should only hold a restricted set of values.

For example:

you may sell clothes or pizza in four sizes: small, medium, large, and extra large.

Of course, you could encode these sizes as integers 1, 2, 3, 4 or characters S, M, L,

and X . But that is an error-prone setup. It is too easy for a variable to hold a wrong

value (such as 0 or m ).

We can define our own enumerated type whenever such a situation arises. An

enumerated type has a finite number of named values. For example:

enum Size { SMALL, MEDIUM, LARGE, EXTRA_LARGE };

Now we can declare variables of this type:

Size s = Size.MEDIUM;

A variable of type Size can hold only one of the values listed in the type declaration,

or the special value null indicates that the variable is not set to any value at all.

Que 11: Is there any data type for Strings in Java? Please explain the basic concept of String in Java?

Ans: No, Java does not support any data type for Strings. The standard Java library contains a predefined class called String.

Example:

Each quoted string is an instance of the String class:

String e = ""; // an empty string

String greeting = "Hello";

Que 12: Write a program to print the first three letters from a given string.

Hint: Use the substring method of the String class.

Ans:

public class SubstringExample{

    public static void main(String args[]){

        String greeting = "Hello";

        String s = greeting.substring(0, 3);

        System.out.println(“First three letters of given String: ” + s);

    }

}

Que 13: What methods String class provides to test equality between two strings? Please provide an example.

Ans: String class provides the following two methods to test the equality which returns true or false.

1. equals(): Case-sensitive check
2. equalsIgnoreCase(): Case insensitive

Examples:

1. String greeting = "Hello";

"Hello".equals(greeting); // returns true

2. String greeting = "hello";

"Hello".equals(greeting); // returns false

"Hello".equalsIgnoreCase(greeting) // returns true

Que 14: What is the significance of NULL and Empty String? Please explain using appropriate examples.

Ans:

Empty: The empty string "" is a string of length 0. We can test whether a string is empty

by calling

if (str.length() == 0)

or

if (str.equals(""))

An empty string is a Java object which holds the string length (namely 0 ) and an

empty contents.

NULL: a String variable can also hold a special value, called null, that indicates that no object is currently associated with the variable.

To test whether a string is null, use the condition

if (str == null)

Sometimes, we need to test that a string is neither null nor empty. Then use the Condition

if (str != null && str.length() != 0)

We need to test that str is not null first. It is an error to invoke a method on a null value.

Que 15: Write down some mostly used String class method names.

Ans:

char charAt(int index)

boolean startsWith(String prefix)

boolean endsWith(String suffix)

int indexOf(String str)

int lastIndexOf(String str)

String replace(CharSequence oldString, CharSequence newString)

String substring(int beginIndex)

String substring(int beginIndex, int endIndex)

String toLowerCase()

String toUpperCase()

String trim()

boolean equals(Object other)

boolean equalsIgnoreCase(String other)

Que 16: What is the use of the Scanner class? Explain using an example.

Ans: Scanner class is used to read input from the command line.

Example:

public class CommandLineInput

{

      public static void main(String args[])

     {

          Scanner in = new Scanner(System.in);

          System.out.print("What is your name? ");

          String name = in.nextLine();

          System.out.print("Your name is: "+name);

          //Get second input

          System.out.print("How old are you? ");

          int age = in.nextInt();

          System.out.print("Your age is: "+age);

      }

}

Que 17: Explain the IF conditional statement using an example.

Ans:

The conditional statement in Java has the form

if (condition) statement

The condition must be surrounded by parentheses.

Example:

if (yourSales >= target)

{

performance = "Satisfactory";

bonus = 100;

}

Que 18: Explain FOR and WHILE loop.

Ans:

While Loop: The while loop executes a statement (which may be a block statement) while a

condition is true. The general form is

while (condition) statement

The while loop will never execute if the condition is false.

Example:

while (balance < goal)

{

    balance += payment;

    double interest = balance * interestRate / 100;

    balance += interest;

    years++;

}

For loop: The for loop is a general construct to support iteration controlled by a counter or

the similar variable that is updated after every iteration.

Example: the following loop prints the numbers from 1 to 10 on the screen.

for (int i = 1; i <= 10; i++)

System.out.println(i);

Que 19: What is the Array? How do we declare and initialize arrays in Java? Explain using an example.

An array is a data structure that stores a collection of values of the same type.

We access each individual value through an integer index.

For example, if a is an array of integers, then a[i] is the i th integer in the array.

Array Declaration:

int[] a; // array a of integers

Array Initialization:

int[] a = new int[100]; // This statement declares and initializes an array of 100 integers.

Que 20: Create a method to insert and print elements from an array.

Ans:

public void arrayExample()

{

// Initialize the array

int[] a = new int[10];

// Get the array length by using length property

int length = a.length;

// Insert values in the array

for (int i = 0; i < a.length; i++)

a[i] = i+10;

//Print the array

for (int i = 0; i < a.length; i++)

System.out.println(a[i]);

}

Que 21: What is the class in Java? Generally what things we can have inside a class?

Ans: A class is a template or blueprint from which objects are made. Think about

classes as cookie cutters. Objects are the cookies themselves. When you construct

an object from a class, you are said to have created an instance of the class.

Generally, a class have fields/variables and methods. All code that we write in Java is inside a class.

Que 22: In OOPs what are the main characteristics of objects?

Ans:

• The object’s behaviour—what can you do with this object, or what methods can

you apply to it?

• The object’s state—how does the object react when you invoke those methods?
• The object’s identity—how is the object distinguished from others that may

have the same behaviour and state?

Que 23: What are the differences between the Procedural program and OOP?

Ans:

In a traditional procedural program, we start the process at the top, with the main

function. When designing an object-oriented system, there is no “top,” and new-

comers to OOP often wonder where to begin. The answer is: Identify your classes

and then add methods to each class.

in an order-processing system, some of the nouns are

Item

Order

Shipping address

Payment

Account

These nouns may lead to the classes Item, Order, and so on.

Que 24: What are the Constructors in Java?

Ans:

In the Java programming language, we use constructors to construct new instances.

A constructor is a special method whose purpose is to construct and initialize

Objects.

Constructors always have the same name as the class name. Thus, the constructor

for the Date class is called Date. To construct a Date object, combine the constructor

with the new operator, as follows:

new Date()

This expression constructs a new object. The object is initialized to the current date and time.

Que 25: Write 5 properties/characteristics of Constructors.

Ans:

• A constructor has the same name as the class.
• A class can have more than one constructor.
• A constructor can take zero, one, or more parameters.
• A constructor has no return value.
• A constructor is always called with the new operator.

Que 26: What happens when we defile class fields as static?

Ans:

If we define a field as static, then there is only one such field per class. In contrast,

each object has its own copy of all instance fields. For example, let’s suppose we

want to assign a unique identification number to each employee. We add an

instance field id and a static field nextId to the Employee class:

class Employee

{

private static int nextId = 1;

private int id;

. . .

}

Every employee object now has its own id field, but there is only one nextId field

that is shared among all instances of the class. Let’s put it another way. If there

are 1,000 objects of the Employee class, then there are 1,000 instance fields id, one for

each object. But there is a single static field nextId . Even if there are no employee

objects, the static field nextId is present. It belongs to the class, not to any individual

object.

Que 27: What are the Static Methods in Java?

Ans:

Static methods are methods that do not operate on objects. For example, the pow method of the Math class is a static method.

The expression Math.pow(x, a) computes the power x a. It does not use any Math object to carry out its task.

In other words, it has no implicit parameter.

We can think of static methods as methods that don’t have this parameter.

Here is an example of such a static method:

public static int getNextId()

{

return nextId; // returns static field

}

To call this method, we supply the name of the class:

int n = Employee.getNextId();

Que 28: What is Overloading?

Ans: some classes have more than one constructor.

For example, you can construct an empty StringBuilder object as

StringBuilder messages = new StringBuilder();

Alternatively, you can specify an initial string:

StringBuilder todoList = new StringBuilder("To do:\n");

This capability is called overloading. Overloading occurs if several methods have the same name (in this case, the StringBuilder constructor method) but different parameters.

The compiler must sort out which method to call. It picks the correct method by matching the parameter types in the headers of the various methods with the types of values used in the specific method call.

A compile-time error occurs if the compiler cannot match the parameters, either because there is no match at all or because there is not one that is better than all others.

Que 29: How can we call one constructor from another?

Ans:

The keyword this refers to the implicit parameter of a method. However, this keyword has a second meaning.

If the first statement of a constructor has the form this(. . .) , then the constructor calls another constructor of the same class.

Here is a typical example:

public Employee(double s)

{

// calls Employee(String, double)

this("Employee #" + nextId, s);

nextId++;

}

When you call a new Employee(60000), the Employee(double) constructor calls the Employee(String, double) constructor.

Using this keyword in this manner is useful—you only need to write common

construction code once.

Que 30: What are the Initialization Blocks? Explain using an example.

Ans:

Class declarations can contain arbitrary blocks of code. These blocks are executed whenever an object of that class is constructed. For example:

class Employee

{

private static int nextId;

private int id;

private String name;

private double salary;

// object initialization block

{

id = nextId;

nextId++;

}

public Employee(String n, double s)

{

name = n;

salary = s;

}

public Employee()

{

name = "";

salary = 0;

}

. . .

}

In this example, the id field is initialized in the object initialization block, no matter which constructor is used to construct an object. The initialization block runs first, and then the body of the constructor is executed.