Java Basics

public class TestExample {  
    public static void main(String args[]) {  
        System.out.println("This is a Simple Example of Java");  
    }  
} 

public class TestExample1 {  
    public static void main(String args[]) {  
        System.out.println("Hello Csharp Corner");  
    }  
}  

• Brackets[]- Opening and closing brackets are used as array element references. These indicate single and multidimensional subscripts.
• Parentheses()- These special symbols are used to indicate function calls and function parameters.
• Braces{}- These opening and ending curly braces mark the start and end of a block of code containing more than one executable statement.
• comma (, )- It is used to separate more than one statement like for separating parameters in function calls.
• Semicolon- It is an operator that essentially invokes something called an initialization list.
• Asterisk (*) It is used to create a pointer variable.

Operators in Java

Operators are special symbols that are used to perform mathematical and logical operations on the operands and return the result. There are several types of operators in java that are used to perform different operations. For example, the (+) operator symbol is used to add two or more operands and returns the addition as a result.

There are many types of operators are available in Java.

Java Assignment Operator

An assignment operator is one of the most used and common operators, which we use to assign a value on its right to the operand on its left.

int a = 5;  
String msg = "Hello"; 

Arithmetic Operators

Arithmetic operators are used to achieving mathematical calculations like algebra. The following table lists arithmetic operators.

int p = 25;      
int q = 15;      
int res = p + q; //addition    
System.out.println("p + q = " + res);      
res = p - q; //substraction          
System.out.println("p - q = " + res);      
res = p * q; //multiplication    
System.out.println("p * q = " + res);      
res = p / q; //division           
System.out.println("p / q = " + res);   

Relational Operators

Relational operators are used to judging against the two operands and give results in a boolean form. The following table lists all the relational operators.

int p = 25;            
 int q = 35;            
boolean res ;            
 res = p == q;            
System.out.println("p == q : " + res);            
res = p != q;            
System.out.println("p != q : " + res);     
res = p > q;     
System.out.println("p is greater than q : " + res);     
res = p >= q;     
System.out.println("p is greater than or equal to q : " + res);     
res = p < q;     
System.out.println("p is less than q : " + res); 

Unary Operators

Java Unary Operators are engaged in a single operand.

int p = 20;      
int res;      
System.out.println( "p : " +p);      
res = ++p;      
System.out.println("++p = " + res);      
res = p++;   

Logical Operators

Logical operators are used to doing logical operations in Java. It operates on two boolean values and returns a boolean value as a result.

boolean p = true;      
boolean q = false;      
boolean res = (p && q);      
System.out.println("p && q = " + res);      
res = (p || q);      
System.out.println("p || q = " + res);      
res = !p;      
System.out.println("!p = " + res); 

Conditional(Ternary) Operators

The Java conditional operators select one of two expressions for evaluation, which is based on the value of the first operands.

int p = 10;      
int q = 20;      
int res = (p > 10) ? p : q;      
System.out.println("result 1 is: " + res);      
res = (q > 10) ? p : q;      
System.out.println("result 2 is: " + res);

Bitwise Operators

Bitwise operators perform bit shift operations on integral types only and not other types.

int b = 7;    
System.out.println("a&b = " + (a & b));    
System.out.println("a|b = " + (a | b));    
System.out.println("a^b = " + (a ^ b));   

For more information about Java Operators Please Click Here.

Variables in Java

The variable is a reserved memory location to hold a value. In other words, when we want to store any value and give it a name, that value takes a reserved space in memory and it’s called a variable.

The variable has any value, which is located in the memory.

How do we declare the Variables in Java?

int x ;     (int is a data type and x is a variable name).  
int y;  
int x, y;  
int x = 4 , y = 5;  
byte p = 65;  
double pi = 3.1415;  
char q = ‘s’ ; 

The complete program is listed below.

public class VariableExampleProgram {  
    int x = 4;     //(int is a data type and x is a variable name).  
    int y = 5;  
    byte p = 65;  
    double pi = 3.1415;  
    char q = 's';  
    public void display() {  
        System.out.println("Value of x =" + x);  
        System.out.println("Value of y =" + y);  
        System.out.println("Value of p =" + p);  
        System.out.println("Value of pi =" + pi);  
        System.out.println("Value of q =" + q);  
    }  
    public static void main(String agrs[]) {  
        VariableExampleProgram var = new VariableExampleProgram();  
        var.display();  
    }  
} 
 

Outpu

Scope of Variables in Java

Global Variables- These variables must be declared inside a class (outside any function). They can be directly accessed anywhere in the class. We can declare class variables anywhere in class, but outside methods.

Syntax

int a;

private String b;

Local Variables- Variables declared inside a method have a method-level scope and can’t be accessed outside the method. Local variables don’t exist after the method’s execution is over

Syntax

public void display() {

int x = 10 ;

}

For more information about Variables in Java Click here.

Data Types in Java

A data type or simply type is an attribute of data that tells the compiler or interpreter how the programmer intends to use the data. For example, a string is a data type that is used to classify text and an integer is a data type used to classify whole numbers.

There are 2 types of Data types in Java

Primitive data type

Java supports eight primitive data type, which is predefined by Java language and named as a keyword.

Data type	Default size	Default value
Byte	1 byte	0
Short	2 byte	0
Int	4 byte	0
Long	8 byte	0L
Float	4 byte	0.0f
Double	8 byte	0.0d
Char	2 byte	‘\u0000’
Boolean	1 bit	false

Maximum value and minimum value

• Byte- Minimum value is -128 (-2^7) and Maximum value is 127 (inclusive)(2^7 -1)
• Short- Minimum value is -32,768 (-2^15) and Maximum value is 32,767 (inclusive) (2^15 -1)
• Int- Minimum value is -2,147,483,648.(-2^31) and Maximum value is 2,147,483,647(inclusive).(2^31 -1)
• Long- Minimum value is -9,223,372,036,854,775,808.(-2^63) and Maximum value is 9,223,372,036,854,775,807 (inclusive). (2^63 -1)
• Char- Minimum value is '\u0000' (or 0) and Maximum value is '\uffff' (or 65,535 inclusive).

Non-Primitive Data Type

Non-Primitive data types are also known as Reference data types. A reference variable is used to refer to any object of the declared type and by default, its value is null. Class object strings and various types of array variables are reference data types.

Java Control Statements

A program executes from top to bottom so a control statement works as a determiner for deciding the next task of the other statements whether to execute or not. Control statements are used to control the flow of execution.

If-statement

If the statement is very basic of all control flow statements. It is used to test the condition if the condition is right. Hence, it returns the output TRUE. It returns the only boolean value true or false

Syntax

if(condition){

// statement.

}

Example

int no = 25;  
if (no > 18) {  
      System.out.println("Number is greater than 18");  
}      

Explanation- In the following example, we are checking if the number is greater than 18 to execute the code.

If-else statement

If – else statement is also used to test the condition but it provides a secondary path of the execution. It returns if statement when the condition is right and when the condition is wrong. Hence, it returns the else statement.

Syntax

If (condition) {

// statement code.

} else {

//statement}

Example

int num = 15;  
if (num % 2 == 0) {  
    System.out.println("this number is even");  
} else {  
     System.out.println("this number is odd");  
} 

Explanation- In the following example, we are checking if the number is divisible by 2 and the remainder is 0 then print the statement "this number is even", else will print "this number is odd".

Nested If-else statement

if-else-if statement checks the one condition from the multiple statements. It is a different statement from others.

Syntax

if(condition1){

// code.

} else if (condition2) {

//code.

}

Else if (condition3){

//code.

}

else {

//code.

}

Example

int marks = 80;  
if (marks < 50) {  
   System.out.println("C grade");  
} else if (marks >= 50 && marks < 60) {  
    System.out.println("C+ grade");  
} else if (marks >= 60 && marks < 70) {  
    System.out.println("B grade");  
} else if (marks >= 70 && marks < 80) {  
    System.out.println("B+ grade");  
} else if (marks >= 80 && marks < 90) {  
    System.out.println("A grade");  
} else if (marks >= 90 && marks < 100) {  
    System.out.println("A+ grade");  
} else {  
    System.out.println("Unfounded");  
} 

Explanation: In the following example, we are checking the grade of the student whose mark is 80 "compiler checks the if conditions, and then if the statement is true the output is A Grade will be printed ", else will print "unfounded".

Switch statement

Java switch statement is also a control flow statement. It is used when we want to be tested for equality against a list of values. The switch statement returns one statement from the multiple conditions.

Syntax

switch(expression){

case value1:

// code.

break; //it is not compulsory(Optional).

case value2;

// code.

break;

default:

// code.

}

Example

char grade = 'C';  
        switch (grade) {  
            case 'A':  
                System.out.println("Excellent");  
                break;  
            case 'B':  
                System.out.println("Very Good");  
                break;  
            case 'C':  
                System.out.println("Good");  
                break;  
            case 'D':  
                System.out.println("Passed");  
            case 'F':  
                System.out.println("Better try again");  
                break;  
            default:  
                System.out.println("Invalid ");  
        }  
        System.out.println("Your grade is " + grade);  

Explanation: In the following example, we are checking the grade of the student whose given grade is C "compiler checks the cases and when the condition is true the output is good Grade will be printed ", and if the given grade is not matched with any case the default statement will be printed.

Loops in Java

Loop control statements are used when code may either be executed a fixed number of times or while some condition is true. Java gives you a choice of three types of loop statements: while, do-while, and for.

The for loop

For statement makes it easier to count the iterations of a loop and works well, where the number of iterations of the loop is referred to before the loop is entered.

Syntax

for(initialization; test condition; increment or decrement)

{

Statements;

}

The main purpose is to repeat the statement when the condition remains true. It is similar to the while loop. Also, for loop specifies an initialization instruction and an increment or decrement of the control variable instruction. Hence, this loop is specially designed to perform a repetitive action with a counter.

How for a loop work?

1. Initialization is executed. This is executed only once.
2. The condition is checked. If it is true, the loop continues otherwise the loop exit and the statement is skipped.
3. Statements are executed. It can be either a single instruction or a block of instructions enclosed within the curly brackets {}.
4. Finally, the increment or decrement of the control variable field is executed and then the loop gets back to step 2.

Example

public class ForLoopExample {  
    public static void main(String[] args) {  
        for (int i = 1; i < 8; i++) {  
            System.out.println("for loop : " + i);  
        }  
    }  
} 

Output

For-each loop

It is a Java 5 feature. For each loop or enhanced for loop is used to traverse an array or collection in Java. It is simple to use than for loop because, in it, we don’t need to increment the value and use subscript notation.

It works based on the element and not an index basis. It returns an element one by one in the defined variable.

Syntax

for(Type var: array)

{

// statements or code.

}

Example

public class ForEachExm {  
        public static void main(String[] args) {  
            int arr[] = {1, 2, 3, 4, 5};  
            for (int s : arr) {  
                System.out.println("Array:" + s);  
            }  
        }  
    } 

Output

while loop

It is used to execute a block of a statement as long as a given condition is true. And when the condition becomes false, the control will come out of the loop. The condition is checked every time at the beginning of the loop.

Syntax

while(test condition)

{

// body of the loop;

}

Here, the test condition is an expression, which expresses how many times the loop run. The body of the loop is a single statement or group of statements, which is enclosed in the braces and they are repeatedly executed till the value of the test condition evaluates to true. The control jumps to the first statement, if the condition initially itself is false, the body of the loop will never be executed. It is also called an entry-control loop.

The execution of the body of the loop depends upon the value of the test condition.

Example

public class WhileLoopExample {  
    public static void main(String[] args) {  
        int n = 1;  
        while (n <= 10) {  
            n++;  
        }  
    }  
} 

Output

Do-while loop

There is another loop control structure that is very similar to the while statement called as do while statement. The only difference is that the expression which determines whether to carry on looping is evaluated at the end of each loop.

Syntax

do {

Statements;

} while (test condition);

In the do-while loop, the loop body is executed at least once, if the condition is false. The loop repeats the body when the condition is true. However, in the while loop, the statement doesn’t execute the body of the loop even once, if the condition is false. This “do-while loop” is also called the exit-control loop.

Example

public class DoWhileExm {  
        public static void main(String[] args) {  
            int n = 1;  
            do {  
                System.out.println("do-while loop : " + n);  
                n++;  
            } while (n < 10);  
        }  
    } 

Output

Java Jump Statements

In Java, jump statements are mainly used to transfer control to another part of our program depending on the conditions. These statements can be used to jump directly to other statements, skip a specific statement, and so on.

1) break

If we want to go out of a loop then we use a break statement. If we use a break statement in a loop then execution will continue with the immediate next statement outside the loop. After a break, all the remaining statements in the loop are skipped.

The break statement is different from the exit. Break jumps the control out of the loop and exit stops the execution of the entire program.

2) continue

Continue statement is sometimes required to skip some part of the loop and to continue the execution with the next loop iteration. The continue statement is mainly used inside the loop helps to bypass the section of a loop and pass the control to the start of the loop to continue the execution with the next loop iteration.

Find more about the break and continue Click Here

Methods in Java

A method is a block of code that only runs when it is called. You can pass data, known as parameters, into a method. Methods are used to perform certain actions, and they are also known as functions. Methods are used for reuse code: define the code once, and use it many times.

Syntax

class <class-name> {

modifier dataType methodName () {

//block of code to be executed } }

//calling the method, from anywhere

className.methodName();

The complete program is listed below.

public class MethodExample {  
        static void myMethod() {  
            System.out.println("Hello World!");  
        }  
        public static void main(String[] args) {  
            myMethod();  
        }  
    } 

The output of the following code generates the following output.

Call by value and Call by reference in Java

Functions can be invoked in two ways: Call by Value or Call by Reference. These two ways are generally differentiated by the type of values passed to them as parameters.

Call by Value

In call by value method, the value of the actual parameters is copied into the formal parameters. we can say that the value of the variable is used in the function call in the call-by-value method. we can not modify the value of the actual parameter by the formal parameter.

In call by value, different memory is allocated for actual and formal parameters since the value of the actual parameter is copied into the formal parameter.

The complete program is listed below.

public class CallByValueExample {  
    public static void main(String[] args) {  
        int a = 30;  
        int b = 45;  
        System.out.println("Before swapping, a = " + a + " and b = " + b);  
        // Invoke the swap method  
        swapFunction(a, b);  
        System.out.println("After swapping, a = " + a + " and b is " + b);  
    }  
  
    public static void swapFunction(int a, int b) {  
        System.out.println("Before swapping(Inside), a = " + a + " b = " + b);  
        int c = a;  
        a = b;  
        b = c;  
        System.out.println("After swapping(Inside), a = " + a + " b = " + b);  
    }  
} 

The output of the following code generates the following output.

Call by Reference

In call by reference, the address of the variable is passed into the function call as the actual parameter. The value of the actual parameters can be modified by changing the formal parameters since the address of the actual parameters is passed. Both the actual and formal parameters refer to the same locations, so any changes made inside the function are reflected in the actual parameters of the caller.

The complete program is listed below.

public class CallByReferenceExample{  
    public static void main(String[] args) {  
        IntWrapper a = new IntWrapper(30);  
        IntWrapper b = new IntWrapper(45);  
        System.out.println("Before swapping, a = " + a.a + " and b = " + b.a);  
        swapFunction(a, b);  
        System.out.println("After swapping, a = " + a.a + " and b is " + b.a);  
    }  
  
    public static void swapFunction(IntWrapper a, IntWrapper b) {  
        System.out.println("Before swapping(Inside), a = " + a.a + " b = " + b.a);  
        // Swap n1 with n2  
        IntWrapper c = new IntWrapper(a.a);  
        a.a = b.a;  
        b.a = c.a;  
        System.out.println("After swapping(Inside), a = " + a.a + " b = " + b.a);  
    }  
}  
  
class IntWrapper {  
    public int a;  
    public IntWrapper(int a) {  
        this.a = a;  
    }  
} 

The output of the following code generates the following output.

List of Data Structures in Java

A data structure is a particular way of organizing data in a computer so that it can be used effectively. For example, we can store a list of items having the same data type using the array data structure. It reduces the time and space complexity.

1) Java Arrays

The array is a data structure used to store homogeneous elements at contiguous locations. The size of an array must be provided before storing data. In an array, elements are accessed using indexes. Each element can be uniquely identified by its index in the array.

For example: If we store the data of the students of a class we can use an array to store that data.

For more about Java, Arrays Click Here

2) Java Stack

Stack data structure represents the LIFO(Last In First Out) mechanism. It is an abstract data type that serves as a collection of elements. The stack data type has two operations that can be performed on the data in the stack.

• Push- Push operation is used to add the element on the top into the collection.
• POP- Pop operation is used for removing the element from the end of the collection.

3) Java Queue

Queue data structure represents the FIFO(First In First Out) mechanism. It is also an abstract data type that serves as a collection of elements. In the queue data structure, the element which will be added last will be the element that will be removed first. The queue has two data types that can be performed on the data in the queue.

• Enqueue- Enqueue operation is used to add the element on the top into the collection.
• Dequeue- Dequeue operation is used to remove the element from the top of the collection.

4) Java Tree

A tree consists of a set of elements (nodes) that can be linked to other elements, sometimes hierarchically and sometimes not. The tree data structure can be defined as a set of nodes that are connected to another node.

5) Java ArrayList Class

This class uses dynamic arrays for storing elements, and arrays are sequentially arranged in the memory. It implements the List interface and extends the AbstractList class. It can contain duplicate elements, and it maintains insertion order. The elements can be accessed using index notation. This class contains various inbuilt methods, which help in making data retrieval and manipulation easy.

To find more about ArrayList in Java Click Here

6) Java Linked List

This class uses a doubly-linked list to store elements. It maintains insertion order, and it can be used as a list, stack, or queue. It implements the List and Dequeue interfaces and extends the Abstract class. The add and remove methods are used to add and delete. The size method returns the number of lists in the list.

7) Java HashMap

This is used to store key-value pairs. It implements the Map interface and is not a part of the collection. HashMap uses the hashing technique to store key-value pairs. The key-value pair is called a bucket. Each bucket is stored in an array in the HashMap class. The hashing function works on the key and returns an index at which the bucket is stored. There are chances of two keys returning the same index upon hashing.

Summary

In this article, we learned about all the basics of the Java programming language. we studied the history of Java, features, set the path of Java, variables, data types, operators and data structures of Java programming language with the syntaxes and examples of Java.