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27.
Java program to perform garbage collection
This program performs
garbage collection. Free memory in java virtual machine is printed and then
garbage collection is done using gc method of RunTime class, freeMemory method
returns amount of free memory in jvm, getRunTime method is used to get
reference of current RunTime object.
import java.util.*;
class GarbageCollection
{
public static void main(String s[]) throws Exception
{
Runtime rs = Runtime.getRuntime();
System.out.println("Free
memory in JVM before Garbage Collection = "+rs.freeMemory());
rs.gc();
System.out.println("Free
memory in JVM after Garbage Collection = "+rs.freeMemory());
}
}
Output of program:
Obviously the amount of
available after garbage collection will be different on your computer. Numbers
are not important, what is important is that amount of memory available is more
than before. You can use this code in your program or projects which uses large
amount of memory or where frequently new objects are created but are required
for a short span of time.
28.
Java program to get ip address
This program prints IP or
internet protocol address of your computer system. InetAddress class of
java.net package is used, getLocalHost method returns InetAddress object which
represents local host.
import java.net.InetAddress;
class IPAddress
{
public static void main(String args[]) throws Exception
{
System.out.println(InetAddress.getLocalHost());
}
}
Output of program:
Output of code prints
computer name/ IP address of computer. Java has a very vast Networking API and
can be used to develop network applications.
29.
Java program to reverse number
This program prints reverse
of a number i.e. if the input is 951 then output will be 159.
import java.util.Scanner;
class ReverseNumber
{
public static void main(String args[])
{
int n, reverse = 0;
System.out.println("Enter the number to reverse");
Scanner in = new Scanner(System.in);
n = in.nextInt();
while( n != 0 )
{
reverse = reverse * 10;
reverse = reverse + n%10;
n = n/10;
}
System.out.println("Reverse of entered number is "+reverse);
}
}
Output of program:
You can also reverse or
invert a number using recursion. You can use this code to check if a number is
palindrome or not, if the reverse of an integer is equal to integer then it's a
palindrome number else not.
30.
Java program to add two matrices
This java program add two
matrices. You can add matrices of any order.
import java.util.Scanner;
class AddTwoMatrix
{
public static void main(String args[])
{
int m, n, c, d;
Scanner in = new Scanner(System.in);
System.out.println("Enter the
number of rows and columns of matrix");
m = in.nextInt();
n = in.nextInt();
int first[][] = new int[m][n];
int second[][] = new int[m][n];
int sum[][] = new int[m][n];
System.out.println("Enter the
elements of first matrix");
for ( c = 0 ; c < m ; c++ )
for ( d = 0 ; d < n ; d++ )
first[c][d] = in.nextInt();
System.out.println("Enter the
elements of second matrix");
for ( c = 0 ; c < m ; c++ )
for ( d = 0 ; d < n ; d++ )
second[c][d] = in.nextInt();
for ( c = 0 ; c < m ; c++ )
for ( d = 0 ; d < n ; d++ )
sum[c][d] = first[c][d] + second[c][d]; //replace '+'
with '-' to subtract matrices
System.out.println("Sum of
entered matrices:-");
for ( c = 0 ; c < m ; c++ )
{
for ( d = 0 ; d < n ; d++ )
System.out.print(sum[c][d]+"\t");
System.out.println();
}
}
}
Output of program:
This code adds two matrix,
you can modify it to add any number of matrices. You can create a Matrix class
and create it's objects and then create an add method which sum the objects,
then you can add any number of matrices by repeatedly calling the method using
a loop.
31.
Java program to transpose matrix
This java program find
transpose of a matrix of any order.
import java.util.Scanner;
class TransposeAMatrix
{
public static void main(String args[])
{
int m, n, c, d;
Scanner in = new Scanner(System.in);
System.out.println("Enter the
number of rows and columns of matrix");
m = in.nextInt();
n = in.nextInt();
int matrix[][] = new int[m][n];
System.out.println("Enter the
elements of matrix");
for ( c = 0 ; c < m ; c++ )
for ( d = 0 ; d < n ; d++ )
matrix[c][d] = in.nextInt();
int transpose[][] = new int[n][m];
for ( c = 0 ; c < m ; c++ )
{
for ( d = 0 ; d < n ; d++ )
transpose[d][c] = matrix[c][d];
}
System.out.println("Transpose
of entered matrix:-");
for ( c = 0 ; c < n ; c++ )
{
for ( d = 0 ; d < m ; d++ )
System.out.print(transpose[c][d]+"\t");
System.out.print("\n");
}
}
}
Output of program:
This code can be used to
check if a matrix symmetric or not, just compare the matrix with it's transpose
if they are same then it's symmetric otherwise non symmetric, also it's useful
for calculating orthogonality of a matrix.
32.
Java program to multiply two matrices
This java program multiply
two matrices. Before multiplication matrices are checked whether they can be
multiplied or not.
import java.util.Scanner;
class MatrixMultiplication
{
public static void main(String args[])
{
int m, n, p, q, sum = 0, c, d, k;
Scanner in = new Scanner(System.in);
System.out.println("Enter the
number of rows and columns of first matrix");
m = in.nextInt();
n = in.nextInt();
int first[][] = new int[m][n];
System.out.println("Enter the
elements of first matrix");
for ( c = 0 ; c < m ; c++ )
for ( d = 0 ; d < n ; d++ )
first[c][d] = in.nextInt();
System.out.println("Enter the
number of rows and columns of second matrix");
p = in.nextInt();
q = in.nextInt();
if ( n != p )
System.out.println("Matrices
with entered orders can't be multiplied with each other.");
else
{
int second[][] = new int[p][q];
int multiply[][] = new int[m][q];
System.out.println("Enter the
elements of second matrix");
for ( c = 0 ; c < p ; c++ )
for ( d = 0 ; d < q ; d++ )
second[c][d] = in.nextInt();
for ( c = 0 ; c < m ; c++ )
{
for ( d = 0 ; d < q ; d++ )
{
for ( k = 0 ; k < p ; k++ )
{
sum = sum + first[c][k]*second[k][d];
}
multiply[c][d] = sum;
sum = 0;
}
}
System.out.println("Product of
entered matrices:-");
for ( c = 0 ; c < m ; c++ )
{
for ( d = 0 ; d < q ; d++ )
System.out.print(multiply[c][d]+"\t");
System.out.print("\n");
}
}
}
}
Output of program:
This is a basic method of
multiplication, there are more efficient algorithms available. Also this approach
is not recommended for sparse matrices which contains a large number of
elements as zero.
33.
Java program to bubble sort
Java program to bubble
sort: This code sorts numbers inputted by user using Bubble sort algorithm.
import java.util.Scanner;
class BubbleSort {
public static void main(String []args) {
int n, c, d, swap;
Scanner in = new Scanner(System.in);
System.out.println("Input
number of integers to sort");
n = in.nextInt();
int array[] = new int[n];
System.out.println("Enter
" + n + "
integers");
for (c = 0; c < n; c++)
array[c] = in.nextInt();
for (c = 0; c < ( n - 1 ); c++) {
for (d = 0; d < n - c - 1; d++) {
if (array[d] > array[d+1]) /* For
descending order use < */
{
swap = array[d];
array[d] = array[d+1];
array[d+1] = swap;
}
}
}
System.out.println("Sorted
list of numbers");
for (c = 0; c < n; c++)
System.out.println(array[c]);
}
}
Complexity of bubble sort
is O(n2) which makes it a less frequent option for arranging in
sorted order when quantity of numbers is high.
Output of program:
You can also use sort
method of Arrays class to sort integers in ascending order but remember that
sort method uses a variation of Quick sort algorithm.
import java.util.Arrays;
class Sort
{
public static void main(String args[])
{
int data[] = { 4, -5, 2, 6, 1 };
Arrays.sort(data);
for (int c: data)
{
System.out.println(c);
}
}
}
·
34.
Java program to open Notepad
How to open Notepad through
java program: Notepad is a text editor which comes with Windows operating
system, It is used for creating and editing text files. You may be developing
java programs in it but you can also open it using your java code.
import java.util.*;
import java.io.*;
class Notepad {
public static void main(String[] args) {
Runtime rs = Runtime.getRuntime();
try {
rs.exec("notepad");
}
catch (IOException e) {
System.out.println(e);
}
}
}
Explanation of code:
getRunTime method is used to get reference of current RunTime object, exec
method can be used to execute commands. You can also specify a file while
opening notepad such as exec("notepad programming.txt") where
'programming.txt' is the file you wish to open, if the file doesn't exist in
current working directory then a dialog box will be displayed to create file.
You can launch other applications using exec method, for example exec("calc")
will launch calculator application. If an application is present in a directory
which is not set in environment variable PATH then you can specify complete
path of application. If you are still using Notepad for Java development it is recommended
to switch to some advanced text editor like Notepad++ or use a development IDE.
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