Reading input and password from command line in Java using java.io.Console - Example tutorial

Java6 added a new utility class for reading input data from character based devices including command line. java.io.Console can be used to read input from command line, but unfortunately it doesn't work on most of IDE like Eclipse and Netbeans. As per Javadoc call to System.Console() will return attached console to JVM, if it has been started interactive command prompt or it will return null if JVM has been started using a background process or scheduler job. Anyway java.io.Console not only provides way to read input from command prompt or Console but also reading passwords from console without echoing it. Console.readPassword() method reads password and returns a character array and password is masked during entering so that any peeping tom can not see your password while you are entering it. here is a code example of How to read password and input from command prompt or console using java.io.Console. By the way apart from Console, you can also use Scanner or BufferedReader to read input from command prompt, as shown in this example.

10 Frequently asked SQL Query Interview Questions

In this article I am giving example of some SQL query which is asked when you go for interview who is having one or two year experience on this field .whenever you go for java developer position or any other programmer position interviewee expect that if you are working from one or two years on any project definitely you come across to handle this database query, so they test your skill by asking this type of simple query.

Question 1: SQL Query to find second highest salary of Employee

Answer : There are many ways to find second highest salary of Employee in SQL, you can either use SQL Join or Subquery to solve this problem. Here is SQL query using Subquery :

select MAX(Salary) from Employee WHERE Salary NOT IN (select MAX(Salary) from Employee );

See How to find second highest salary in SQL for more ways to solve this problem.

Question 2: SQL Query to find Max Salary from each department.

Answer :

SELECT DeptID, MAX(Salary) FROM Employee  GROUP BY DeptID.

Question 3:Write SQL Query to display current date.

 Ans:SQL has built in function called GetDate() which returns current timestamp.

SELECT GetDate();

Question 4:Write an SQL Query to check whether date passed to Query is date of given format or not.

Ans: SQL has IsDate() function which is used to check passed value is date or not of specified format ,it returns 1(true) or 0(false) accordingly.

SELECT  ISDATE('1/08/13') AS "MM/DD/YY";

It will return 0 because passed date is not in correct format.

Question 5: Write a SQL Query to print the name of distinct employee whose DOB is between 01/01/1960 to 31/12/1975.

Ans:

SELECT DISTINCT EmpName FROM Employees WHERE DOB  BETWEEN ‘01/01/1960’ AND ‘31/12/1975’;

Question 6:Write an SQL Query find number of employees according to gender  whose DOB is between 01/01/1960 to 31/12/1975.

Answer : SELECT COUNT(*), sex from Employees  WHERE  DOB BETWEEN ‘01/01/1960 ' AND ‘31/12/1975’  GROUP BY sex;

Question 7:Write an SQL Query to find employee whose Salary is equal or greater than 10000.

Answer : SELECT EmpName FROM  Employees WHERE  Salary>=10000;

Question 8:Write an SQL Query to find name of employee whose name Start with ‘M’

Ans: SELECT * FROM Employees WHERE EmpName like 'M%';

Question 9: find all Employee records containing the word "Joe", regardless of whether it was stored as JOE, Joe, or joe.

Answer : SELECT  * from Employees  WHERE  upper(EmpName) like upper('joe%');

Question 10: Write a SQL Query to find  year from date.

Answer :  SELECT YEAR(GETDATE()) as "Year";

Hope this article will help you to take a quick practice whenever you are going to attend any interview and not have much time to go into the deep of each query.

Other Interview Questions posts from Java67 Blog

10 Tricky Java Interview Questions 

10 Java Web Service Interview questions

10 Android Interview Questions 

10 Java Collection and Generics interview questions

10 JDBC Interview Questions in Java

An Example of Overriding Equals, HashCode and CompareTo method in Java

Though modern IDE like Eclipse, IntelliJ or Netbeans allows you to generate equals, hashCode and compareTo methods for your value classes, it's equally important, you know how to do that by hand. By overriding equals and hashcode method by yourself, you know how they work, what kind of errors you can get, and most importantly, it's expected form you, as a Java programmer in any core Java interview. More often, you would see a coding question in Java, which ask you to override equals(), hashcode(), compare() and compareTo() methods for a value class. Since I have already shared some tips on How to override compareTo method in Java, and couple of example of writing your own comparator in Java, here I am sharing another simple example of overriding equals and hashCode methods. If you know rules of overriding equals and hashCode, you might know that, whenever you override equals, you must have to override hashCode, otherwise your object will not behave properly on various collection classes e.g. Map or Set, which uses equals, compareTo, hashCode to implement there invariants e.g. Set implementations should not allow any duplicates.

How to Split String in Java with Example using Regular Expression

String class provides split() method to split String in Java, based upon any delimiter, e.g. comma, colon, space or any arbitrary method. split() method splits string based on delimiter provided, and return a String array, which contains individual Strings. Actually, split() method takes a regular expression, which in simplest case can be a single word. split() is also overloaded method in java.lang.String class and its overloaded version takes a limit parameter which is used to control how many times pattern will be applied during splitting process. if this limit is positive n, then pattern will be applied at most n-1 times, if it's negative or zero than split operation is applied any number of time. For example, if we split String "First,Second,Third" on comma and provide limit as 2 then pattern will run one time, and split() will return String array with 2 Strings, "First" and "Second,Third". Since this method accepts a Java regular expression, it throws PatternSyntaxException, if syntax of regular expression is invalid.

How to replace String in Java - character substring replaceAll example

String class in Java provides several methods to replace characters, CharSequence and substring from String in Java. Since String is immutable in Java, every time you performance an operation on String either replacement or removing white space from String, it generates a new String object. There are four overloaded method to replace String in Java :

replace(char oldChar, char newChar)

replace(CharSequence target, CharSequence replacement)

replaceAll(String regex, String replacement)

replaceFirst(String regex, String replacement)

Out of these, 2nd one which takes a CharSequence is added on Java 1.5. CharSequence is actually a super interface for String, StringBuffer and StringBuilder in Java, which means you can pass any of String, StringBuffer or StringBuilder Object as argument to this replace method. replaceFirst() and replaceAll() are very powerful and accepts regular expression. replaceFirst() only replace first match, while replaceAll replaces all matches with replacement String provided.

Difference between wait vs notify vs notifyAll in Java

wait, notify, and notifyAll methods are used for inter thread communication in Java. wait() allows a thread to check for a condition, and wait if condition doesn't met, while notify() and notifyAll() method informs waiting thread for rechecking condition, after changing state of shared variable. One good example of how wait and notify method works is Producer consumer problem, where one thread produces, and wait if bucket is full; and other thread consumes and wait if bucket is empty. Both Producer and Consumer thread, notify each other as well. Producer thread notifies consumer thread after inserting an item in shared queue, while consumer thread notify producer, after consuming item from queue. Though Both notify() and notifyAll()  are used to notify waiting threads, waiting on shared queue object, but there are some subtle difference between notify and notifyAll in Java. Well, when we use notify(), only one of the sleeping thread will get notification, while in case of notifyAll(), all sleeping thread on that object will get notified. This concept confuses many Java programmers, both beginners and experienced alike, Infact this is one of three question which is very popular on wait and notify concept, along with why wait and notify is defined in Object class and why wait and notify called from synchronized method. In this article we will focus on difference between wait, notify, and notifyAll method in Java.

How to convert Java String to int or Integer - valueOf vs parseInt

There are 3 main ways to convert String to int in Java, using constructor of Integer class, parseInt() method of java.lang.Integer and Integer.valueOf() method. Though all those method returns instance of java.lang.Integer, which is a wrapper class for primitive int value, it's easy to convert Integer to int in Java. From Java 5, you don't need to do anything, autoboxing will automatically convert Integer to int. For Java 1.4 or lower version, you can use intValue() method form java.lang.Integer class, to convert Integer to int. As name suggest, parseInt() is the core method to convert String to int in Java. parseInt() accept a String which must contain decimal digits and first character can be an ASCII minus sign (-) to denote negative integers. parseInt() throws NumberFormatException, if provided String is not convertible to int value. By the way parseInt is an overloaded method and it's overloaded version takes radix or base e.g. 2,8,10 or 16, which can be used to convert binary, octal, hexadecimal String to int in Java. Integer.valueOf() is another useful method to convert String to Integer in Java, it offers caching of Integers from -128 to 127. Internally, valueOf() also calls parseInt() method for String to int conversion. In this Java programming tutorial, we will see all three ways to convert String to int value in Java.