InstanceOfJava

How to read values from properties file in java example

Posted by: Instanceofjava Posted date: 12:39 AM / comment : 0 Basic Java Example programs , java load properties file example , java programming interview questions

To store configurable parameters, .properties file will be used in java.
We can Store data in key value pair (key=value).
Re compilation not required if we change any keys or values in properties file.
Used for internationalization and to store frequently changeable values.

java.util.Properties class is sub class of Hashtable.
We can read / load the propertied file using InputStream.
InputStream inputStream = getClass().getClassLoader().getResourceAsStream(properties_FileName);
Create a maven project, under resources create one .properties file and load this file in main class using getClass().getClassLoader().getResourceAsStream(properties_FileName).
Lets see an example java program on java read properties file from resource folder or how to read values from properties file in java example or how to get values from properties file in java.

#1: Create a maven project:

java read properties file from classpath

Create properties file:

#1: Java example program to get values from properties file in java

package com.instanceofjava.propertiesfile;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.Date;
import java.util.Properties;
/**
*
* @author www.instanceofjava.com
* @category: java example programs
*
* Write a java example program to read/ load properties file
*
*/
public class ReadPropertiesFile {
public Properties getProperties() throws IOException {
InputStream inputStream=null;
Properties properties = new Properties();
try {
String propFileName = "config.properties";
inputStream = getClass().getClassLoader().getResourceAsStream(propFileName);
if (inputStream != null) {
properties.load(inputStream);
} else {
throw new FileNotFoundException("property file '" + propFileName + "' not found
in the classpath");
}
} catch (Exception e) {
System.out.println("Exception: " + e);
} finally {
inputStream.close();
}
return properties;
}
public static void main(String[] args) throws IOException {
ReadPropertiesFile obj= new ReadPropertiesFile();
Properties properties=obj.getProperties();
// get the each property value using getProperty() method
System.out.println("username: "+properties.getProperty("username"));
System.out.println("password: "+properties.getProperty("password"));
System.out.println("url: "+properties.getProperty("url"));
}
}

Output:

username: user1
password: abc123
url: www.instanceofjava.com

Java finally block after return statement

Posted by: Instanceofjava Posted date: 10:56 PM / comment : 0 Core java Interview Questions

finally block will be executed always even exception occurs.
If we explicitly call System.exit() method then only finally block will not be executed if exit() call is before finally block.
There are few more rare scenarios where finally block will not be executed.

When JVM crashes
When there is an infinite loop
When we kill the process ex:kill -9 (on unix)
Power failure, hardware error or system crash.
And as we discussed System.exit().

Other than these conditions finally block will be executed always.
finally block is meant to keep cleaning of resources. Placing code other than cleaning is a bad practice
What happens if we place finally block after return statement? or
Does finally block will execute after return statement??
As per the above rules Yes finally will always execute except any interruption like System.exit() or all above mentioned conditions

Program #1 : Java example program which explains how finally block will be executed even after a return statement in a method.

package com.instanceofjava.finallyblockreturn;
/**
* By: www.instanceofjava.com
* program: does finally gets executed after return statement??
*
*/
public class FinallyBlockAfterReturn {
public static int Calc(){
try {
return 0;
} catch (Exception e) {
return 1;
}
finally{
System.out.println("finally block will be executed even when we
place after return statement");
}
}
public static void main(String[] args) {
System.out.println(Calc());
}
}

Output:

finally block will be executed even when we place after return statement
0

Can we place return statement in finally??

Yes we can place return statement in finally and finally block return statement will be executed.
But it is a very bad practice to place return statement in finally block.

Program #2 : Java example program which explains finally block with return statement in a method.

How to subtract minutes from current time in java

Posted by: Instanceofjava Posted date: 11:44 PM / comment : 0 Java 8 , java programming interview questions

We have discussed about how to subtract hours from java 8 using LoclaDateTime class in java.
How to subtract N hours from current date time using java 8
Now we will see how to subtract minutes from current date time in java.
How to subtract minutes from current time in java / How to subtract minutes from time in java.
Lets see an example java program which will subtract minutes from java date time
How to subtract minutes from current time in java

Program #1 : Java Example Program to subtract minutes from given string formatted date time using java 8.

package java8;
/**
* By: www.instanceofjava.com
* program: how to subtract minutes from date time using java 8
*
*/
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
public class SubtractMinutesJava{
public static void main(String[] args) {
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
String currentTime= "2017-10-19 22:00:00";
System.out.println("Before subtraction of minutes from date: "+currentTime);
LocalDateTime datetime = LocalDateTime.parse(currentTime,formatter);
datetime=datetime.minusMinutes(30);
String aftersubtraction=datetime.format(formatter);
System.out.println("After 30 minutes subtraction from date: "+aftersubtraction);
}
}

Output:

Before subtraction of minutes from date: 2017-10-19 22:00:00
After 30 minutes subtraction from date: 2017-10-19 21:30:00

Program #2 : Java Example Program to subtract seconds from given string formatted date time using java 8.

package java8;
/**
* By: www.instanceofjava.com
* program: how to subtract seconds from date time using java 8
*
*/
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
public class SubtractSecondsJava{
public static void main(String[] args) {
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
String currentTime= "2017-10-19 22:00:00";
System.out.println("Before subtraction of seconds from date time: "+currentTime);
LocalDateTime datetime = LocalDateTime.parse(currentTime,formatter);
datetime=datetime.minusSeconds(30);
String aftersubtraction=datetime.format(formatter);
System.out.println("After 30 seconds subtraction from date time: "+aftersubtraction);
}
}

Output:

Before subtraction of seconds from date time: 2017-10-19 22:00:00
After 30 seconds subtraction from date time: 2017-10-19 21:59:30

Program #3 : Java Example Program to subtract seconds from current date time using java 8.

how to subtract minutes from java date time

How to subtract N hours from current date time using java 8

Posted by: Instanceofjava Posted date: 11:22 PM / comment : 0 java programming interview questions , java8

We have already seen how to subtract number of days from java using calendar and using java 8.
How to subtract X days from a date using Java calendar and with java 8
Now we will discuss here how to subtract hours from java 8 localdatetime.
Some times we will get out date time in string format so we will convert our string format date to java 8 LocaDateTime object.
We can user DateTimeFormatter to tell the format of date time to LocalDateTime class.
LocalDateTime datetime = LocalDateTime.parse(currentTime,formatter);
LocalDateTime has minusHours(numberOfHours) method to subtract hours from date time.
Lets see an example java program to subtract hours from java date time using java 8 LocalDateTime class.
How to subtract hours from java 8 date time.

Program #1 : Java Example Program to subtract hours from given string formatted date time using java 8.

package java8;
/**
* By: www.instanceofjava.com
* program: how to subtract hours from date time using java 8
*
*/
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
public class SubstractHoursJava{
public static void main(String[] args) {
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
String currentTime= "2017-10-19 22:00:00";
System.out.println("Before subtraction of hours from date: "+currentTime);
LocalDateTime datetime = LocalDateTime.parse(currentTime,formatter);
datetime=datetime.minusHours(4);
String aftersubtraction=datetime.format(formatter);
System.out.println("After 4 hours subtraction from date: "+aftersubtraction);
}
}

Output:

Before subtraction of hours from date: 2017-10-19 22:00:00
After 4 hours subtraction from date: 2017-10-19 18:00:00

Now we will see how to subtract one hour from current date time in java using java 8

Program #2 : Java Example Program to subtract one hour from given current date time using java 8.

package java8;
/**
* By: www.instanceofjava.com
* program: how to subtract hours from date time using java 8
*
*/
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
public class SubtractOneHour {
public static void main(String[] args) {
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd H:mm:ss");
LocalDateTime datetime = LocalDateTime.now();
System.out.println("Before subtraction of hours from date: "+datetime.format(formatter));
datetime=datetime.minusHours(1);
String aftersubtraction=datetime.format(formatter);
System.out.println("After 1 hour subtraction from date: "+aftersubtraction);
}
}

Output:

Before subtraction of hours from date: 2017-10-19 23:14:12
After 1 hour subtraction from date: 2017-10-19 22:14:12

C program to insert an element in an array

Posted by: Instanceofjava Posted date: 11:15 AM / comment : 1 C language interview programs

Program to insert an element in an array at a given position
C program to insert an element in an array without using function

Program #1: Write a c program to insert an element in array without using function

#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
int insarray[100], pos, c, n, value;
printf("Enter number of elements of array\n");
scanf("%d", &n);
printf("Enter all %d elements\n", n);
for (c = 0; c < n; c++)
scanf("%d", &insarray[c]);
printf("Enter the specific position where you wish to insert an element in array\n");
scanf("%d", &pos);
printf("Enter the value to insert\n");
scanf("%d", &value);
for (c = n - 1; c >= pos - 1; c--)
insarray[c+1] = insarray[c];
insarray[pos-1] = value;
printf("Resultant array is\n");
for (c = 0; c <= n; c++)
printf("%d\n", insarray[c]);
getch();
}