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An abstract method is the one that does not have a body. It contains only a method signature with a semi colon and, an abstract keyword before it.public abstract myMethod();To use an abstract method, you need to inherit it by extending its class and provide implementation (body) to it. If a class contains at least one abstract method, you must declare it abstract.Example Live Demoimport java.io.IOException; abstract class MyClass { public abstract void display(); } public class AbstractClassExample extends MyClass{ public void display(){ System.out.println("subclass implementation of the display method"); } public static void main(String ... Read More
Abstraction is a process of hiding the implementation details from the user, only the functionality will be provided to the user. In other words, the user will have the information on what the object does instead of how it does it.Since all the methods of the interface are abstract and the user doesn’t know how a method is written except the method signature/prototype. Using interfaces, you can achieve (complete) abstraction.Abstraction in interfacesAn interface in Java is a specification of method prototypes. Whenever you need to guide the programmer or, make a contract specifying how the methods and fields of a ... Read More
Yes, you can use false as 0 to match.Let us first create a table −mysql> create table DemoTable804 ( Id varchar(100) ); Query OK, 0 rows affected (0.66 sec)Insert some records in the table using insert command −mysql> insert into DemoTable804 values('101John'); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable804 values('Carol1002'); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable804 values('1000'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable804 values('1010Bob'); Query OK, 1 row affected (0.10 sec)Display all records from the table using select statement −mysql> select *from DemoTable804;This ... Read More
To set default values for columns while creating a table, DEFAULT. Let us first see an example and create a table. As you can see below, while creating the table, we have set DEFAULT −mysql> create table DemoTable803 ( UserId int DEFAULT 101, UserName varchar(100) DEFAULT 'Chris' ); Query OK, 0 rows affected (1.18 sec)Insert some records in the table using insert command. For the values we are not inserting, the default values will get set automatically −mysql> insert into DemoTable803 values(102, 'Chris'); Query OK, 1 row affected (0.34 sec) mysql> insert into DemoTable803(UserName) ... Read More
Use CONCAT() to concatenate records whereas IFNULL() to check for NULL values.Let us first create a table −mysql> create table DemoTable802 ( FirstName varchar(100), LastName varchar(100) ); Query OK, 0 rows affected (1.01 sec)Insert some records in the table using insert command −mysql> insert into DemoTable802 values('Adam', 'Smith'); Query OK, 1 row affected (0.23 sec) mysql> insert into DemoTable802 values('Carol', NULL); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable802 values(NULL, 'Taylor'); Query OK, 1 row affected (0.09 sec) mysql> insert into DemoTable802 values(NULL, NULL); Query OK, 1 row affected (0.21 sec)Display ... Read More
For this, use ORDER BY IF().Let us first create a table −mysql> create table DemoTable801 ( Score int ); Query OK, 0 rows affected (0.69 sec)Insert some records in the table using insert command −mysql> insert into DemoTable801 values(30); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable801 values(99); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable801 values(45); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable801 values(55); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable801 values(99); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable801 values(69); ... Read More
Let us first create a table −mysql> create table DemoTable800 ( Value int ); Query OK, 0 rows affected (0.59 sec)Insert some records in the table using insert command. Here, we have inserted 5 similar values −mysql> insert into DemoTable800 values(10); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable800 values(10); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable800 values(10); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable800 values(10); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable800 values(10); Query OK, 1 row affected (0.10 sec)Display all ... Read More
Whenever you want to restrict the type parameter to subtypes of a particular class you can use the bounded type parameter. If you just specify a type (class) as bounded parameter, only sub types of that particular class are accepted by the current generic class. These are known as bounded-types in generics in Java.Defining bounded-types for classYou can declare a bound parameter just by extending the required class with the type-parameter, within the angular braces as −class Sample ExampleIn the following Java example the generic class Sample restricts the type parameter to the sub classes of the Number classes using ... Read More
The CONCAT() method is used to concat, whereas GROUP_CONCAT() is used to concatenate strings from a group in a single string.Let us first create a table −mysql> create table DemoTable799 ( UserId int, UserName varchar(100), UserAge int ); Query OK, 0 rows affected (0.56 sec)Insert some records in the table using insert command −mysql> insert into DemoTable799 values(101, 'John', 21); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable799 values(102, 'Chris', 26); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable799 values(101, 'Robert', 23); Query OK, 1 ... Read More
Let’s see when the #1054 error occurs in MySQL. While inserting a varchar value, if you will forget to add single quotes, then this error will arise. Following is the error −mysql> insert into DemoTable798 values(100, Adam); ERROR 1054 (42S22): Unknown column 'Adam' in 'field list'You need to use single quotes around the string value to fix this error as shown below −mysql> insert into DemoTable798 values(100, ’Adam’);Let us first create a table −mysql> create table DemoTable798 ( StudentId int, StudentName varchar(100) ); Query OK, 0 rows affected (0.51 sec)Insert some records in the ... Read More