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JOptionPane.showInputDialog in Java Example

By Dinesh Thakur

JOptionPane Class is present in javax.swing package. This class is used to display simple dialog boxes to get the text input From the user. showInputDialog method is a static method of JOptionPane class. This method uses single parameter that specifies the prompting message that is displayed in the dialog box. In this program message is- “Enter the Number for Right Angle Trangle Height?” This method returns string value. Syntax- public static String showInputDialog (String s).

Here is the Java Example for JOptionPane.showInputDialog:

import javax.swing.*; 
 public class JOptionPaneExample 
 { 
              public static void main(String[] args) 
       { 
              System.out.println("Print Right Angle Trangle"); 
           String Number = JOptionPane.showInputDialog("Enter the Number for Right Angle Trangle Height?"); 
              int n = Integer.parseInt(Number); 
              int c = 1; 
              for(int i=0;i<n;i++) 
                  { 
                      c++; 
                      for(int j=1; j<c; j++) 
                          { 
                                System.out.print(j+" "); 
                          } 
                                System.out.println(); 
                   } 
          } 
 }

JOptionPane.showInputDialog

3×3 Matrix in Java Example

By Dinesh Thakur

Just like one-dimensional arrays, a two-dimensional array can also be passed to a method and it can also be returned from the method. The syntax is similar to one-dimensional arrays with an exception that an additional pair of square brackets is used. Two-dimensional Array is specified by taking additional square brackets i.e. “[][]”.

Arrays are generally initialized with the new command, which creates a new instance of a reference data type. There is only one way to reference the items: by using a subscript to indicate which element number to access. The number used to reference the specific element of an array is called the component. In Java, the subscripts always start at zero and go to the length of the array minus 1. The new command initializes the array to null characters. Reference to elements in the array is by subscript or component. All the elements of an array must be of the same type.

Example:

int c[][]=new int[3][3];
The left index indicates row number and right index indicates the column number.

Here the number of rows represent the number of integer references to which “c” is pointing. The number of columns represents the length of the integer array to which each element of the array of references points.

 

import java.io.*;
class Matrix3x3
{
    public static void main(String args[]) throws IOException
    {
        BufferedReader BR=new BufferedReader(new InputStreamReader (System.in));
        int Number[][]=new int[3][3];
        int i,j;
        String m;
        System.out.println("Enter Elements for Matrix 3x3 :");
        for(i=0;i<=2;i++)
        {
            for(j=0;j<=2;j++)
            {
                m=BR.readLine();
                Number[i][j]=Integer.parseInt(m);
            }
        }
        System.out.println("Elements in Matrix are : ");
                                System.out.println("");
        for(i=0;i<=2;i++)
        {
            for(j=0;j<=2;j++)
            {
                System.out.print(Number[i][j]+"\t");
            }
            System.out.println();
        }
    }
}

3x3 Matrix in Java

Integer.parseInt(string) in Java Example

By Dinesh Thakur

Integer.parseInt() method is used for converting the data fed in form of strings into integer form.

import java.io.*;
class IntegerParseInt
{
    public static void main(String args[])
    throws IOException
    {
        BufferedReader BF= new BufferedReader(new InputStreamReader (System.in));
        int Number[]=new int[5];
        int i;
        String m;
        System.out.println("Enter 5 Numbers :");
        for(i=0;i<=4;i++)
        {
            m=BF.readLine();
            Number[i]=Integer.parseInt(m);
        }
        System.out.println("Your Entered 5 Numbers are :");
        for(i=0;i<=4;i++)
        {
            System.out.println(Number[i]);
        }
    }
}

Integer.parseInt(string) in Java

Static Method and Static Variable in Java Example

By Dinesh Thakur

Since the string variable str is static, it is initialized to “This is second line displayed” (static variables are initialized before an object is initiated). Then, the static block is executed which will invoke the disp() method displaying the message: “This is first line displayed”. Static() method can be invoked without the need of any object. In main(), again disp() method is called with the string str (This is second line displayed). After that an object SMV is made, and it will get a member str2 initialized to “This is last line displayed”. Then disp() is called with SMV. str2 which displays: This is last line displayed on the screen [Read more…] about Static Method and Static Variable in Java Example

Tail Recursion in java

By Dinesh Thakur

Tail recursion occurring when the recursive call is at the end of the recursive instruction. This eliminates the potential problem of stack overflow. A call is tail recursive if nothing has to be done after the call returns. i.e. when the call returns, the returned value is immediately returned from the calling method.

 

Reverse the Digits of a Number Using Recursion | Java Example

By Dinesh Thakur

In this program, user is asked a number to enter which is stored in integer form in variable n. The value entered is say 1023.Now, this value of variable n is passed to parameter x by invoking revers() method. In revers() method, x is divided by 10 and the remainder is displayed (% returns remainder). When 1023 is divided by 10, the remainder will be 3 which is displayed on the screen. Then, again revers() is invoked with value 102/10 i.e. with 102 (because the output of dividing two integers is also an integer). 102 is assigned to variable x. Again, 102 is divided by 10 and the remainder is displayed. The remainder this time will be 2 which is displayed. Again revers() method is invoked with 10/10 i.e. which 1. And the process continues until value of x becomes 0.

Here is the Java Example for ReverseDigits:

import java.io.*; 
 class ReverseDigits 
 { 
             void revers(int x) 
             { 
                         if(x==0) return; 
                         else 
                         { 
                                     System.out.print(x%10); 
                                     revers(x/10); 
                         } 
             } 
             public static void main(String args[]) 
             throws IOException 
             { 
                         ReverseDigits Digit = new ReverseDigits(); 
                         BufferedReader bf=new BufferedReader(new InputStreamReader(System.in)); 
                         String h; 
                         int n; 
                         System.out.print("Enter a number to Reverse : "); 
                         h=bf.readLine(); 
                         n=Integer.parseInt(h); 
                         System.out.print("The  Reverse Number is : "); 
                         Digit.revers(n); 
             } 
 }

Reverse the Digits of a Number Using Recursion

Recursion in Java with Example

By Dinesh Thakur

Recursion occurs when a function calls itself in its own body. That is, in the body of the function definition there is a call to itself. When the function calls itself in its body, it results in an infinite loop. So, there has to be an exit condition in every recursive program.

The case in which the recursion ends is called a base case. In every recursive program, the problem is broken into small pieces so as to bring it closer to the base case.

Methods/Functions have locally defined variables (or objects) which have no existence outside the function. Each time a function is invoked recursively, a new set of variables (or objects) are created. Although they have the same names, their values are preserved till the end of the recursion. So, to implement recursion, the language has to take the help of stack to keep track of objects and statements of each recursive call.

Demonstrating the Concept of Recursion

class ConceptofRecursion 
 { 
             void display(int x,int y) 
             { 
                         if(x<1) return; 
                         System.out.println("Value of x : "+ x ); 
                         display(x-1,y+1); 
                         System.out.println("Value of y :"+y); 
             } 
             public static void main(String args[]) 
             { 
                         ConceptofRecursion Recursion = new ConceptofRecursion(); 
                         Recursion.display(5,1); 
             } 
 }

 

Recursion in Java

As, we can see in the above program, that the method display () is invoked with two arguments 5 and 1 which will be assigned to parameters x and y respectively. In display ()  method, value of x is displayed which prints following message on the screen : Value of x: 5

Then again display ()  is invoked with values 4 and 2 (because value of x is decremented and value of y is incremented by 1 while invoking the display (). But because of the recursive call, one statement of the program couldn’t execute, that statement is:

System.out.println(“Value of y :”+y);

So, the message: Value of y : 1 is pushed on to the stack.

By the recursive call, the values 4 and 2 will be assigned to parameters x and y respectively. Here, value of x is displayed which prints following message on the screen:

Value of x: 4

Again, display ()   is invoked with values 3 and 3 (because value of x is decremented and value of y is incremented by 1 while invoking the display () . But again, because of the recursive call, the following statement couldn’t execute:

System.out.println(“Value of y :”+y);

So, the message: Value of y: 2 is pushed on to the stack (above the message Value of y : 1) and so on. Hence, 5 messages will be pushed onto the stack which couldn’t execute as shown:

Disadvantages of Recursion

 

1. The problem of stack overflow occurs in case of infinite recursion

 

2. Recursion can be slower to run than simple iteration.

 

3. The recursive version is usually less efficient because of having to push and pop values on and off the run-time stack, so iteration is quicker.

 

Advantages of Recursion

 

1. It is easier to code a recursive solution.

 

2. The recursive code is usually smaller, more concise, and more elegant.

 

3. There are some real time problems that are very difficult to solve without recursion.

Passing Arguments to a Method in Java Example

By Dinesh Thakur

There are two ways of passing arguments to a method (function/subroutine):

1. Call by Value

This method copies the value of an argument into the formal parameter of the method. Therefore, changes made to the parameter of the method are limited to that method only and there is no impact of changes on the argument. That is, when control returns back to the caller method, earlier values of the arguments will be seen.

2. Call by Reference

In this method, a reference to an argument (not the value of the argument) is passed to the parameter. Inside the method, this reference is used to access the actual argument specified in the call. This means that changes made to the parameter will affect the actual argument also. When the control returns back to the caller method, the changes made in the method can be seen in the arguments in the caller method too.

In Java, when we pass a simple type to a method, it is passed by value. When we create a variable of a class, we are only creating a reference to an object. Thus, when we pass this reference method, the parameter that receives it will refer to the same object as that referred by the argument. This means that objects are passed to methods by reference.

 

Demonstration of Pass by Reference

 

 

class Passby

{

            int a,b;

            void setdata(int x,  int  y)

            {

                        a  =  x;

                        b = y;

            }

            void display(Passby m)

            {

                        m.a =m.a+10;

                        m.b=m.b-5;

            }

}

class PassbyRef

{

            public static void main(String args[])

            {

                        Passby Ref =new Passby();

                        Ref.setdata(50,100);

                        System.out.println(“Before Function Call: a=” + Ref.a +” b= ” + Ref.b) ;

                        Ref.display(Ref);

                        System.out.println(“After Function Call: a=” + Ref.a +” b= ” + Ref.b) ;

            }

}

 

Output

 

Before Function Call: a = 50 b= 100

After Function Call: a = 60 b= 95

 

In above program, first an instance of class Passbyby name Ref is made. The value of its data members a and b are set to 50 and 100 respectively by invoking setdata() method. After that by invoking display (), the instance Ref itself is sent as argument to parameter m. Since, we know that objects are passed to methods by reference, any changes made in the data members of parameter m will also effect the argument Ref. In the display (), the value of data member a is incremented by 10 and the value of data member is decremented by 5. The same effects will be seen in the argument Ref when the control returns back to the main() method.

 

Demonstration of Pass by Value

 

 

class PassbyValue

{

            public static void main(String args[])

            {

                        int a =50, b=100;

                        System.out.println(“Before Function Call : a = ” +a+ ” b = “+b);

                        chng(a,b);

                        System.out.println(“After Function Call : a = ” +a+ ” b = “+b);

            }

            static void chng(int x, int y)

            {

                        x=x+10;

                        y=y-5;

            }

}

 

Output:

Before Function Call: a= 50 b= 100

After Function call: a= 50 b= 100

 

When we pass a simple type to a method, it is passed by value. So, any changes made to the data in the method are limited to that method only and the data retains its older values when returns back to the caller.

Write Data to a File Using Scanner in Java Example

By Dinesh Thakur

Here is the Java Example for Write Data to a File Using Scanner:

import java.util.Scanner; 
 import java.io.*; 
 public class WriteFileUsingScanner 
 { 
               public static void main(String[] args)throws Exception 
        { 
               String p=setpath(); 
               write(p); 
               System.out.println("\n\n\t\t1 File Created Successfully"); 
         } 
                   static String setpath() 
             { 
                      Scanner read =new Scanner(System.in); 
                      String path; 
                      System.out.println("Enter the Path You want to Set \n\t"); 
                      return read.nextLine(); 
             } 
                      static void write(String path)throws Exception 
                  { 
                         Scanner read =new Scanner(System.in); 
                         FileOutputStream fos=new FileOutputStream(path); 
                         System.out.println("\n\t\tEnter character  ('y') to stop writing.\n\n"); 
                         int ch; 
                         String data; 
                         byte b[]; 
                         boolean flag=true; 
                         byte eof=(char)('y'); 
                         while(true) 
                                { 
                                   data=read.nextLine(); 
                                   b=data.getBytes(); 
                                   for(int i=0;i<b.length;i++) 
                                       { 
                                           if(b[i]==eof) 
                                              { 
                                                  flag=false; 
                                                  break; 
                                              } 
                                                   fos.write(b[i]); 
                                        } 
                                              if(flag==false) 
                                                 break; 
                                                fos.write((byte)('\n')); 
                                  } 
                                                fos.close(); 
                      } 
 }

Write Data to a File Using Scanner

Java Program Which Can List All Files in a Given Directory | Java Example

By Dinesh Thakur

File is a predefined class present in java.io package. listFiles method is a predefined method of File class.

This method is used to show the list of files present in the specified directory.
Syntax- public File[] listFiles()

Here is the Java Example for List All Files in a Given Directory  :

import java.io.*; 
 public class ListAllFiles 
 { 
               public static void main(String args[]) 
        { 
              File f = new File("c:\\"); 
              File[] f1 = f.listFiles(); 
              for (int AllFiles=0; AllFiles<f1.length; AllFiles++) 
                    { 
                         System.out.println(f1[AllFiles].toString()); 
                    } 
         } 
 }

List All Files in a Given Directory

Copy Data From One File to Another File in Java Example

By Dinesh Thakur

There are numerous classes available for reading/writing bytes from/to file, memory or even a network socket. We have already given a brief overview of byte stream classes and we shall now discuss them in detail.

The FilelnputSteam and the FileOutputStream classes are used to read and write bytes sequentially from a file. The FilelnputStream class extends InputStream class and therefore inherits all its methods. However, it does not define any new methods of its own. Similarly, the FileOutputStream class inherits all the methods of the OutputStream class which it extends and does not define any new methods of its own.

In order to open a file for input, create a FilelnputStream object. For this, the FilelnputStream class provides the following constructors.

FilelnputStream(String fileName)
FilelnputStream(File fileObj)
Here, fileName specifies the name ofthe file and fileObj is a File object that describes the file. If the file to be opened doesnot exist, both these constructors throw java.io.FileNotFoundException.

In order to open a file for output, create a FileOutputStream object. For this, the
FileOutputStream class provides the following constructors.
FileOutputStream(File fileObj)
FileOutputStream(String fileName)
FileOutputStream(File fileObj, boolean append)
FileOutputStream(String fileName, boolean append)
Here, fileName specifies the name ofthe file and fileObj is a File object that describes the file. If the file dose not exist, new file would be created. If the file exists, the first two constructors overwrite the existing contents of the file. To retain the existing contents and append the new data at the end of the file, use the last two constructors and let the second argument append to true. A java.io.FileNotFoundException is thrown if
• File exists but is a directory rather thana regular file.
• File doesnot exist but cannot be created.
• File cannot be opened for any other reason.

Now let us consider a program that demonstrates how to write bytes to the file CopyDataFiletoFile.dat using FileOutputStream and read-them back from the same file using the FilelnputStream.

Here is the Java Example for Copy Data From One File to Another:

import java.io.*; 
 class CopyDataFiletoFile  
 { 
              public static void main(String args[])throws IOException 
         { 
               FileInputStream Fread =new FileInputStream("Hello.txt"); 
               FileOutputStream Fwrite=new FileOutputStream("Hello1.txt") ; 
               System.out.println("File is Copied"); 
               int c; 
               while((c=Fread.read())!=-1) 
               Fwrite.write((char)c); 
               Fread.close(); 
               Fwrite.close(); 
          } 
 }

 

Copy Data From One File to Another File

Append Text to File Java Example

By Dinesh Thakur

The constructor of FileOutputStream class is overload, when we pass Boolean argument (true) in the constructor of FileOutputStream, then the new text append in the file.

FileOutputStream file = new FileOutputStream (“Hello.txt”, true);

Here is the Java Example for Append Text to File:

import java.io.*; 
 class AppendTexttoFile 
 { 
           public static void main(String args[])throws IOException 
        { 
                  try 
            { 
                    BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); 
                    FileOutputStream file = new FileOutputStream("Hello.txt",true); 
                    System.out.println("Enter the text and Type 'y' to Terminate"); 
                    char ch; 
                    while((ch=(char)br.read())!='y') 
                    file.write(ch); 
                    file.close(); 
             } 
                     catch(IOException e) {} 
          } 
 }

Append Text to File Java Example

Reading Data From File in Java Example

By Dinesh Thakur

FileInputStream is a is present in java.io package and is the child class of InputStream class. It reads data in the form of bytes from a text file.

FileInputStream file = new FileInputStream(“Hello.txt”) ; Here file is the object of FileInputStream class and points to “Hello.txt” file and if the file is not present then program is terminated by generating fileNotFoundException.

Read data from the file.

Here is the Java Example for Reading Data From File:

import java.io.*; 
 class ReadDataFile 
 { 
            public static void main(String args[]) 
       { 
             try 
          { 
                  FileInputStream file=new FileInputStream("Hello.txt"); 
                  System.out.println("Show the File Contents "); 
                  int ch; 
                  while((ch=file.read())!=-1) 
                  System.out.print((char)ch); 
                  file.close(); 
           } 
                  catch(IOException e) {} 
        } 
 }

Reading Data From File

Create a File and Write Data in Java Example

By Dinesh Thakur

FileOutputStream is a class present in java.io package and child class of outputstream class. It Stores data in the form of bytes. It is used to create a text file.

In this program we are using BufferedReader class which is child class of Reader class is used to read data from keyboard.
BufferedReader file = new BufferedReader(new InputStreamReader(System.in));
Here file is the object of the FileOutputStream class that points to ” test txt file, if the file is not present it creates a new file.
FileoutputStream file=new FileoutputStream(“Hello.txt”);
ch=(char)br.read()
file.write(ch);
To close the file we have to close the associated streams.
file.close();

Here is the Java Example for Create a File and Write Data in Java:

import java.io.*; 
 class WriteDataFile 
 { 
            public static void main(String args[]) 
        { 
                 try 
              { 
                    BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); 
                    FileOutputStream file = new FileOutputStream("Hello.txt"); 
                    System.out.println("Enter text and Type 'y' to Terminate"); 
                    char c; 
                    while((c=(char)br.read())!='y') 
                    file.write(c); 
                   file.close(); 
                    System.out.println("File is Created"); 
              } 
                    catch(IOException e){} 
        } 
 }

Create a File and Write Data in Java

 

Java.util.Arrays.sort(char[]) Method Example | Java Example

By Dinesh Thakur

Array.sort():- It is a predefined method of Array class present in java.util package. It used to sorts all the elements of an array in ascending order.

Syntax:- static void sort(array)

Here is the Java Example for Sorting Strings into Alphabetical Order:

import java.util.*; 
 import java.io.*; 
 public class ArraySort 
 { 
                       public static void main(String args[]) 
            { 
                            System.out.print("Please Enter String for Sorting : "); 
                            Scanner s=new Scanner(System.in); 
                            String s1=s.nextLine(); 
                            s1=s1.toLowerCase(); 
                            char[] SortingStrings=s1.toCharArray(); 
                            Arrays.sort(SortingStrings); 
                            String sorted=new String(SortingStrings); 
                            System.out.println("After Sorting Strings into Alphabetical Order : "+sorted); 
             } 
 }

Java.util.Arrays.sort