Tag: Java

Java Log and StackTrace

log method using stackTrace in Java


   A custom log() method can used to print a message with a details like which class which function 
   called the log at which line number. It is useful for debugging.





  1 public class Main {
  2     public static void func() {
  3         Log.log("\"log msg\"");
  4     }
  5
  6     public static void main(String[] args) {
  7         func();
  8         Log.log("printing log in main");
  9     }
 10 }
 11
 12 class Log {
 13
 14     public static void log(String s) {
 15         StackTraceElement[] stackTrace = Thread.currentThread().getStackTrace();
 16         String className = stackTrace[2].getClassName();
 17         String caller = stackTrace[2].getMethodName();
 18         int lineNo = stackTrace[2].getLineNumber();
 19         System.out.println("[class-name : " + className + "],  [caller-function : "
 20                 + caller + "], [ line-no : "+ lineNo+ "], " + s);
 21     }
 22 }






Output:


[class-name : Main],  [caller-function : func], [ line-no : 3], “log msg”
[class-name : Main],  [caller-function : main], [ line-no : 8], printing log in main





	


	



			
				


			

			
Java Date and Calendar Class.
		
	
	

		


Get the Current Date:


Date today = new Date();
System.out.println(“Current date: “ + today);
OUTPUT:
date: Sat May 04 02:29:59 IST 2019
 


Difference between dates:


Date currentTime = new Date();          Thread.sleep(3000);            //Waits for 3 seconds.         Date newTime = new Date();              


//diferrence in ms. long msDelay = newTime.getTime() – currentTime.getTime(); 







Check Whether Time Interval has Passed:




public static void main(String[] args) throws Exception {    Date startTime = new Date();    long deadLine = startTime.getTime() + 3000;  //    +3 seconds
    Date deadLineDate = new Date(deadLine);    Date currentTime = new Date();


    int secondsCount = 0;
    while(!currentTime.after(deadLineDate))// Check whether currentTime is after deadLineDate    {


       Thread.sleep(1000); // Sleep for 1 sec.


       secondsCount++;


       System.out.println(secondsCount + ” seconds have passed.”);


       currentTime = new Date();


    }


    System.out.println(“Reached DeadLine!”);}





Output:


1 seconds have passed. 2 seconds have passed. 3 seconds have passed. Reached DeadLine!

Using getTime()
public class Main {   public static void main(String[] args) {


    Date startTime = new Date();


    long deadLine = startTime.getTime() + 3000;  //    +3 seconds
    Date deadLineDate = new Date(deadLine);    Date currentTime = new Date();


    int secondsCount = 0;
    while(currentTime.getTime() < deadLineDate.getTime())// Check whether currentTime is after deadLineDate    {


       Thread.sleep(1000); // Sleep for 1 sec.


       secondsCount++;


       System.out.println(secondsCount + ” seconds have passed.”);


       currentTime = new Date();


    }


    System.out.println(“Reached DeadLine!”);


   }}

before()
equals()
also work with same syntax as after()




Various get and set methods:












get methods


Date currentTime = new Date();int hours = currentTime.getHours();  // hours passed since midnight. 


int mins = currentTime.getMinutes(); // hours passed since midnight.int secs = currentTime.getSeconds(); // seconds passed since midnight.














set methods






Date yearStartTime = new Date(); 


yearStartTime.setHours(0); 


yearStartTime.setMinutes(0); 


yearStartTime.setSeconds(0); 


yearStartTime.setDate(1); // First day of month


yearStartTime.setMonth(0); // January (months are indexed from 0 to 11)













Calendar class:








Calendar calendar = new GregorianCalendar(2017, 0 , 25);


GregorianCalendar calendar = new GregorianCalendar(2017, Calendar.JANUARY , 25);





set the time 10:30:15  1 Jan 2019


public static void main(String[] args) {   Calendar calendar = new GregorianCalendar();   calendar.set(Calendar.YEAR, 2019);   calendar.set(Calendar.MONTH, 0);   calendar.set(Calendar.DAY_OF_MONTH, 1);   calendar.set(Calendar.HOUR_OF_DAY, 10);   calendar.set(Calendar.MINUTE, 30);   calendar.set(Calendar.SECOND, 15);    System.out.println(calendar.getTime());}



Output:


Tue Jan 01 10:30:15 IST 2019
—————————————————————-










public static void main(String[] args) {   Calendar calendar = new GregorianCalendar(2019, Calendar.JANUARY , 1);   calendar.set(Calendar.HOUR, 10);   calendar.set(Calendar.MINUTE, 30);   calendar.set(Calendar.SECOND, 15);    calendar.add(Calendar.MONTH, –2); // Date will automatically adjust into 2018.   System.out.println(calendar.getTime());}

output:
Thu Nov 01 10:30:15 IST 2018
——————————————————————
roll() : This method will make change only in particular part, In this example 
only Month will be reduced to Nov but years and other time will not be changed. 

public static void main(String[] args) {   Calendar calendar = new GregorianCalendar(2019, Calendar.JANUARY , 1);   calendar.set(Calendar.HOUR, 10);   calendar.set(Calendar.MINUTE, 30);   calendar.set(Calendar.SECOND, 15);    calendar.roll(Calendar.MONTH, –2); // Date will automatically adjust into 2018.   System.out.println(calendar.getTime());}
Output:
Fri Nov 01 10:30:15 IST 2019
——————————————————————






get and set:






calendar.set(Calendar.HOUR, 10);calendar.set(Calendar.MINUTE, 30);calendar.set(Calendar.SECOND, 15); System.out.println(“Year: “ + calendar.get(Calendar.YEAR));System.out.println(“Month: “ + calendar.get(Calendar.MONTH));
——————————————————————-






date format:






SimpleDateFormat dateFormat = new SimpleDateFormat(“EEEE, MMMM d, yyyy”);
Calendar calendar = new GregorianCalendar(2019, Calendar.JANUARY , 1);
System.out.println(dateFormat.format(calendar.getTime()));

output:
Tuesday, January 1, 2019







Difference of days between two dates:


long diff_ms = date1.getTime() – date2.getTime();


days = diff_ms / (24 * 60 * 60 * 1000);




















		
	
	


	



			
				


			

			
Java Collections
		
	
	

		






Interface
Class/implementation
Description




List
 ArrayList
 List




 LinkedList
 List




 Vector
 Vector




 Stack
 Stack




 Set  
 HashSet
 Set




 TreeSet
 Set




 SortedSet
 Sorted set




Map
 HashMap
Map/dictionary




 TreeMap
 Map/dictionary




 SortedMap
 Sorted dictionary




 Hashtable
 Hash-table









Declaration Syntax:


List<String> list = new ArrayList<String>();


Set<String> set = new HashSet<String>();


Map<String, String> map = new HashMap<String, String>();


ADD Elements Syntax:


list.add(“techBuddha”);


set.add(“techBuddha”);


map.put(“key”, “techBuddha”);




Traversing Collection Syntax:




Iterator<String> iterator = list.iterator();while (iterator.hasNext())   {


      String text = iterator.next();      System.out.println(text);}


—————————————————-


Iterator<String> iterator = set.iterator();


while (iterator.hasNext())       {      String text = iterator.next();      System.out.println(text);}


——————————————————


Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator();while (iterator.hasNext()){      Map.Entry<String, String> pair = iterator.next();      String key = pair.getKey();                  String value = pair.getValue();              System.out.println(key + “:” + value);


}


—————————————————–


Traversing Collection with ShortHand Fast For Loop:


 for (String text : list) {     System.out.println(text); }


——————————————————-


 for (String text : set) {     System.out.println(text); }


——————————————————-


for (Map.Entry<String, String> pair : map.entrySet()){     String key = pair.getKey();                           String value = pair.getValue();                      System.out.println(key + “:” + value);}


——————————————————-



Methods for Set:








Operation
Method




Add element(s)
add(), addAll()




Remove element(s)
remove(), removeAll()




Check for the presence of element(s)
contains(), containsAll()











Methods for Map:








Operation
Method




Get a set of all pairs
entrySet()




Get a set of all keys
keySet()




Get a set of all values
values()




Add a pair
put(key, value)




Get the value for the specified key
get(key)




Check whether the specified key is present
containsKey(key)




Check whether the specified value is present
containsValue(value)




Check whether the Map is empty
isEmpty()




Clear the Map
clear()




Remove the value for the specified key
remove(key)












Collection Methods:


ArrayList<Integer> list = new ArrayList<Integer>();

sort()     : Collection.sort(list);
max()      : Collection.max(list);
min()      : Collection.min(list);
reverse()  : Collection.reverse(list);
shuffle()  : Collection.shuffle(list);
swap()     : Collection.swap(list, i, j);


unmodifiableList() : creates immutable arrayList from an array.
List<String> weekEndDays = Collections.unmodifiableList(new ArrayList<>(Arrays.asList(saturday, sunday)));

disjoint() : It checks whether two collections intersect, returns false if intersection is non null otherwise true.

ArrayList<String> list1 = new ArrayList<>(Arrays.asList(sunday, monday, tuesday));ArrayList<String> list2 = new ArrayList<>(Arrays.asList(saturday, sunday));
Collection.disjoint(list1, list2); // will return false, sunday is common.



Collection Initialization:


public static  Set join(Set a, Set b) 


{  


    /*Double braces initialization*/


    return new HashSet() {{ addAll(a); addAll(b); }} 


}