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Object Oriented Programming Articles
Page 552 of 589
Is main method compulsory in Java?
To compile a program, you doesn’t really need a main method in your program. But, while execution JVM searches for the main method. In the Java the main method is the entry point Whenever you execute a program in Java JVM searches for the main method and starts executing from it.The main method must be public, static, with return type void, and a String array as argument.public static int main(String[] args){ }You can write a program without defining a main it gets compiled without compilation errors. But when you execute it a run time error is generated saying “Main method ...
Read MoreExplain widening with objects in Java.
Java provides various datatypes to store various data values. It provides 7 primitive datatypes (stores single values) namely, boolean, byte, char, short, int, long, float, double and, reference datatypes (arrays and objects).Type Casting/type conversion − Converting one primitive datatype into another is known as type casting (type conversion) in Java. You can cast the primitive datatypes in two ways namely, Widening and, Narrowing.Widening − Converting a lower datatype to a higher datatype is known as widening. In this case the casting/conversion is done automatically therefore, it is known as implicit type casting. In this case both datatypes should be compatible ...
Read MoreExplain narrowing with object in Java.
Java provides various datatypes to store various data values. It provides 7 primitive datatypes (stores single values) namely, boolean, byte, char, short, int, long, float, double and, reference datatypes (arrays and objects).Type Casting/type conversion −Converting one primitive datatype into another is known as type casting (type conversion) in Java. You can cast the primitive datatypes in two ways namely, Widening and, Narrowing.Narrowing − Converting a higher datatype to a lower datatype is known as narrowing. In this case the casting/conversion is not done automatically, you need to convert explicitly using the cast operator “( )” explicitly. Therefore, it is known ...
Read MoreWhat is instance variable hiding in Java?
Whenever you inherit a superclass a copy of superclass’s members is created at the subclass and you using its object you can access the superclass members.If the superclass and the subclass have instance variable of same name, if you access it using the subclass object, the instance variables of the subclass hides the instance variables of the superclass irrespective of the types. This mechanism is known as field hiding or, instance variable hiding.But, since it makes code complicated field hiding is not recommended.ExampleIn the following example we have two classes Super and Sub one extending the other. They both have ...
Read MoreWhat are the default array values in Java?
In Java arrays are the reference types which stores multiple elements of the same datatype. You can create an array just like an object using the new keyword −type[] reference = new type[10];or, directly using the flower brackets ({}).int [] myArray = {10, 20, 30, 40, 50}When you create instance variables in Java you need to initialize them, else the compiler will initialize on your behalf with default values.Similarly, if you create an array as instance variable, you need to initialize it else the compiler initializes with default values which are −Integer − 0Byte − 0Float − 0.0Boolean − falseString/Object ...
Read MoreJava Program to find all angles of a triangle
To find the angles of a triangle we can use sin/cosine rules according to cosine rule −cos A = (b^2 + c^2 - a^2)/2bcwhere A, B , C are the vertices and a, b, c are the sides of the given triangle then, angles of the triangle when the sides a, b, c given are −angleAtA = acos((b^2 + c^2 - a^2)/(2bc)) angleAtB = acos((a^2 + c^2 - b^2)/(2ac)) angleAtC = acos((a^2 + b^2 - c^2)/(2ab))
Read MoreHow to insert a DATALINK object into a table using JDBC?
A DATALINK object represents an URL value which refers to an external resource (outside the current database/data source), which can be a file, directory etc.You can store a DATALINK into an SQL table using the setURL() method of the PreparedStatement interface. This method accepts an integer value representing an index of the bind variable, an URL object and, inserts the given URL object in the column represented by the bind variable in the specified index.ExampleLet us create a table with name tutorials_data in MySQL database using CREATE statement as shown below −CREATE TABLE tutorials_data ( tutorial_id INT PRIMARY KEY ...
Read MoreWhat is ODBC?
ODBC stands for Oracle Database Connectivity. It is an API which is used to access different databases.The OFBC driver uses the Open Database connectivity interface provided by Microsoft to communicate with the databases. It is independent of Databases and platforms and operating systems. Once you develop an application using ODBC you can run it on other platforms with little change in Data access code. ODBC uses SQL syntax and it is based on Open call level interface.
Read MoreWhat is the difference between include action and include directive in JSP?
include action lets you insert files into the page being generated. The syntax looks like this −Unlike the include directive, which inserts the file at the time the JSP page is translated into a servlet, this action inserts the file at the time the page is requested.
Read MoreHow to print a date using JSP Expression?
Following example shows a JSP Expression printing date on the browser − A Comment Test Today's date: The above code will generate the following result −Today's date: 11-Sep-2010 21:24:25
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