Java Syntax cheatsheet

javaSyntax.java

import java.util.Scanner;
import java.util.ArrayList;


public class hello {
    public static void main(String[] args) throws Exception
    {

      
      Scanner reader = new Scanner(System.in);
      String name =reader.nextLine();
      System.out.println(name);
      double a=45.23;
      int ab=a.intValue(); //45
      Scanner sc = new Scanner(System.in);
                  BigInteger a = sc.nextBigInteger();            
                         BigInteger b = sc.nextBigInteger();            
        BigInteger sum=a.add(b);
        BigInteger prod=a.multiply(b);
        System.out.println(sum);
        System.out.println(prod);
      Scanner sc=new Scanner(System.in);
            int x=sc.nextInt();
            double y=sc.nextDouble();
            sc.nextLine();
            String s=sc.nextLine();


            System.out.println("String: "+s);
            System.out.println("Double: "+y);
            System.out.println("Int: "+x);
  
      int count=1;
       TreeSet ts = new TreeSet();       
        for(int i=0;i<=word.length();i++)
        {
            for (int c=0;c<=word.length()-i;c++){
                if(word.substring(i,c+i).length()==3){
                     ts.add(word.substring(i,c+i));
            }
        }
      while(scanner.hasNext()){
            String a=scanner.nextLine();
            System.out.println(count+" "+a);
            count++;
        }
      int number = Integer.parseInt(reader.nextLine());
        while(number!=answer){


            if(number>answer) {
                System.out.println("Guessed Number is lesser" +" Guesses made = "+count);
            }
            else{
                System.out.println("Guessed Number is greater" +" Guesses made = "+count);
            }
            number = Integer.parseInt(reader.nextLine());
            count++;

        }
         ArrayList<String> wordList = new ArrayList<String>();
        

        wordList.add("First");
        wordList.add("Second");
        Collections.sort(wordList);
         for (String word : wordList) {
        System.out.println( word );
    }
    ArrayList<Integer> numbers = new ArrayList<Integer>();
    // JOptionsPane.showMessageDialog
    numbers.add(4);
    /*
    next() v/s nextLine() : 
    next() returns till a complete token is given. 
    nextLine() advances the scanner till '\n' is present and moves the cursor down. next() keeps the cursor there only
    */
    
    numbers.add(8);

    // tries to remove the number from the index 4, does not work as expected!
    numbers.remove(4);

    // this removes the number 4 from the list
    numbers.remove(Integer.valueOf(4));

    }
    public static int randNum(int min,int max) {
        Random rand = new Random();
        int randomNum = rand.nextInt((max - min) + 1) + min;
        return randomNum;

    }

    //OOPS in Java

    public class Person{
      int age;
      int name;

      public Person(String initnames){
        this.name=initnames;
        this.age=0;

      }

      public String toString(){
        return this.name+" "+this.age;
      }
      public void setage(int agebyUser){
        this.age=agebyUser;
      }
      public int getage(){
        return this.age;
      }
      public boolean isAdult(){
        if (this.age>18){
          return true;
        }
        else{
          return false;
        }
      }
      //Object as argument to method
      public boolean isAcceptedAsMember(Person person) {
        if ( person.age() < this.age ) {
            return false;
        }

        return true;
    }
    }

    public class Man extends Person{
    private String gender;

    public Man(String name,int age) {
        super(name, age);
        this.gender = gender;
    }

    public String getMotorType() {
        return motorType;
    }

    public String getGender(){
      return gender;
    }

        @Override
    public String toString() {
        return super.toString() + "\n  And my personal message again!";
    }
    }

    //Customer - Order Inheritance example : 
    public class Customer{
      private String name;
      private String address;

      public Customer(String name,String address){
        this.name=name;
        this.address=address;
      }
      public String getName(){
        return name;
      }
      public String getAddress(){
        return address;
      }
      public void setAddress(String address){
          this.address=address;
      }
    }

    public Order extends Customer{
      private String product;
      private Customer customer;
      private String amount;

      public Order(String product,String amount,String name,String)
      {
        super(name,address);
        this.product=product;
        this.amount=amount;
      }
        public Tilaus(Customer customer, String product, String amount) {
        this.customer = customer;
        this.product = product;
        this.amount = amount;
    }


      public String getProduct(){
        return product;
      }
      public String getAmount(){
        return amount;
      }

      public String mailingaddress(){
        return this.getName()+" "+this.getAddress();
      }

       public String mailingAddressSecondPart() {
        return this.customer.getName() + "\n" + this.customer.getAddress();
    }

    }

   
}

//Socket Programming :  

import java.net.*;
public class IdentifyHostNameIP {
public static void main(String[] args) {
for (int i = 0; i < args.length; i++) {
try {
InetAddress address = InetAddress.getByName(args[i]);
System.out.print("Host name: " + address.getHostName() + " ");
System.out.println("IP address: " + address.getHostAddress());
}
catch (UnknownHostException ex) {
System.err.println("Unknown host or IP address " + args[i]);
}
}
}
}

import java.io.*;
import java.net.*;
import java.util.Scanner;

public class client {
    private DataOutputStream toServer;
    private DataInputStream fromServer;

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

    public client()
    {
        Scanner reader = new Scanner(System.in);
        double radius = reader.nextInt();

        try {
            Socket socket = new Socket("localhost", 8000);
            fromServer = new DataInputStream(socket.getInputStream());
            toServer = new DataOutputStream(socket.getOutputStream());
        }
        catch(IOException ex){
            System.out.println("Unknown network issue");
        }
    try{
        toServer.writeDouble(radius);
        toServer.flush();
        double area = fromServer.readDouble();
        System.out.println("Area is : "+area);
            }
            catch(IOException ex){
                System.err.println(ex);
            }
        }
    }
// ^ client.java

// server.java (added gui for fun )
import java.awt.*;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Date;
import javax.swing.*;

public class server extends JFrame {

    private JTextArea jta = new JTextArea();

    public static void main(String[] args) {
        new server();
    }
    public server()
    {
        //GUI
        setLayout(new BorderLayout());
        add(new JScrollPane(jta), BorderLayout.CENTER);

        setTitle("server");
        setSize(500,300);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);

        //server Code
        try {
            ServerSocket serverSocket = new ServerSocket(8000);//Establish this server with the port 8000
            jta.append("server started at " + new Date() + "\n");


            //Allows server to listen for connections
            Socket socket = serverSocket.accept();
            InetAddress inetAddress = socket.getInetAddress();
            System.out.println("Client's host name is " +
                    inetAddress.getHostName());

            //Data streams for writing/reading data into the connected socket from above
            DataInputStream inputFromClient = new DataInputStream(socket.getInputStream());
            DataOutputStream outputToClient = new DataOutputStream(socket.getOutputStream());


            while(true) {
                double radius = inputFromClient.readDouble();
                double area = radius * radius * Math.PI;

                outputToClient.writeDouble(area);

                jta.append("Radius recieved from client: " + radius + "\n");
                jta.append("Area found: " + area + "\n");
            }
        }
        catch(IOException ex){
            System.err.println(ex);
        }
    }
}
      
Theory :  


GUI : 

import javax.swing.*;
public class MyFrame {
  public static void main(String[] args) {
    JFrame frame = new JFrame("Test Frame");
    frame.setSize(400, 300);
    frame.setVisible(true);
    frame.setDefaultCloseOperation(
      JFrame.EXIT_ON_CLOSE);
  }
   }


// Add a button into the frame
frame.getContentPane().add(
  new JButton("OK"));


JPanel p = new JPanel();
p.add(new JButton("OK"));