 public class Stack{
  
  //basic functions
  private int [] arr;
  private int sizeOfArray = 0;  //mein nahi chahta duniya is element ko istemaal kare. 
  private int sizeOfStack = 0;
  private int tos = -1;
  
  
  public void initialize(int size){
    this.arr = new int[size];
    this.sizeOfArray = size;
    this.sizeOfStack = 0;
    this.tos = -1;
  }
  
  
  //constructor
  
  public Stack(){
    this.initialize(5);
  }
  
  public Stack(int size){
    this.initialize(size);
  }
  //Exception
  private void stackIsFullException() throws Exception{
    if(this.sizeOfArray == this.sizeOfStack){
      throw new Exception("stackIsFull-TalkToPratyaksha");
    }
  }
  
  private void stackIsEmptyException() throws Exception{
    if(this.sizeOfArray == 0){
      throw new Exception("stackIsEmpty");
    }
  }
    
  //basic function
  public boolean isEmpty(){
    return this.sizeOfStack == 0;
  }
  
  public int size(){
    return this.sizeOfStack;
  }
  
  public void push(int val)throws Exception{ //jo bhi function Exception throw ker sakte hai, unko infected
  //fucntion bolte hai and unke sath throws Exception likhna padega hame compulsory
    stackIsFullException();
    this.tos++;
    this.arr[tos] = val;
    this.sizeOfStack++;
    
  }
  
  public int pop()throws Exception{
    stackIsEmptyException();
    int val = this.top();
    this.arr[this.tos] = 0;
    this.tos--;
    this.sizeOfStack--;
    return val;
    
  }
  
  public int top()throws Exception{
    stackIsEmptyException();
    return this.arr[this.tos];
  }
  
  public static void main(String[] args)throws Exception{
    Stack st = new Stack(9);
    for(int i=1; i<=5; i++){
      st.push(i*10); 
    }
    
    st.push(60);
    
    while(st.size() != 0){
      System.out.println(st.pop() + "");
    }
  }
}

created 3 years ago by Pratyaksha Maheshwari

Java online compiler

Write, Run & Share Java code online using OneCompiler's Java online compiler for free. It's one of the robust, feature-rich online compilers for Java language, running the Java LTS version 17. Getting started with the OneCompiler's Java editor is easy and fast. The editor shows sample boilerplate code when you choose language as Java and start coding.

Taking inputs (stdin)

OneCompiler's Java online editor supports stdin and users can give inputs to the programs using the STDIN textbox under the I/O tab. Using Scanner class in Java program, you can read the inputs. Following is a sample program that shows reading STDIN ( A string in this case ).

import java.util.Scanner;
class Input {
    public static void main(String[] args) {
    	Scanner input = new Scanner(System.in);
    	System.out.println("Enter your name: ");
    	String inp = input.next();
    	System.out.println("Hello, " + inp);
    }
}

Adding dependencies

OneCompiler supports Gradle for dependency management. Users can add dependencies in the build.gradle file and use them in their programs. When you add the dependencies for the first time, the first run might be a little slow as we download the dependencies, but the subsequent runs will be faster. Following sample Gradle configuration shows how to add dependencies

apply plugin:'application'
mainClassName = 'HelloWorld'

run { standardInput = System.in }
sourceSets { main { java { srcDir './' } } }

repositories {
    jcenter()
}

dependencies {
    // add dependencies here as below
    implementation group: 'org.apache.commons', name: 'commons-lang3', version: '3.9'
}

About Java

Java is a very popular general-purpose programming language, it is class-based and object-oriented. Java was developed by James Gosling at Sun Microsystems ( later acquired by Oracle) the initial release of Java was in 1995. Java 17 is the latest long-term supported version (LTS). As of today, Java is the world's number one server programming language with a 12 million developer community, 5 million students studying worldwide and it's #1 choice for the cloud development.

Syntax help

Variables

short x = 999; 			// -32768 to 32767
int   x = 99999; 		// -2147483648 to 2147483647
long  x = 99999999999L; // -9223372036854775808 to 9223372036854775807

float x = 1.2;
double x = 99.99d;

byte x = 99; // -128 to 127
char x = 'A';
boolean x = true;

Loops

1. If Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
  // code
} else {
  // code
}

Example:

int i = 10;
if(i % 2 == 0) {
  System.out.println("i is even number");
} else {
  System.out.println("i is odd number");
}

2. Switch:

Switch is an alternative to If-Else-If ladder and to select one among many blocks of code.

switch(<conditional-expression>) {    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
...    
    
default:     
 //code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition. Usually for loop is preferred when number of iterations is known in advance.

for(Initialization; Condition; Increment/decrement){  
    //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while(<condition>){  
 // code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {
  // code 
} while (<condition>);

Classes and Objects

Class is the blueprint of an object, which is also referred as user-defined data type with variables and functions. Object is a basic unit in OOP, and is an instance of the class.

How to create a Class:

class keyword is required to create a class.

Example:

class Mobile {
    public:    // access specifier which specifies that accessibility of class members 
    string name; // string variable (attribute)
    int price; // int variable (attribute)
};

How to create a Object:

Mobile m1 = new Mobile();

How to define methods in a class:

public class Greeting {
    static void hello() {
        System.out.println("Hello.. Happy learning!");
    }

    public static void main(String[] args) {
        hello();
    }
}

Collections

Collection is a group of objects which can be represented as a single unit. Collections are introduced to bring a unified common interface to all the objects.

Collection Framework was introduced since JDK 1.2 which is used to represent and manage Collections and it contains:

Interfaces
Classes
Algorithms

This framework also defines map interfaces and several classes in addition to Collections.

Advantages:

High performance
Reduces developer's effort
Unified architecture which has common methods for all objects.

Collection	Description
Set	Set is a collection of elements which can not contain duplicate values. Set is implemented in HashSets, LinkedHashSets, TreeSet etc
List	List is a ordered collection of elements which can have duplicates. Lists are classified into ArrayList, LinkedList, Vectors
Queue	FIFO approach, while instantiating Queue interface you can either choose LinkedList or PriorityQueue.
Deque	Deque(Double Ended Queue) is used to add or remove elements from both the ends of the Queue(both head and tail)
Map	Map contains key-values pairs which don't have any duplicates. Map is implemented in HashMap, TreeMap etc.