Yes, a double value can be cast to a byte.
−
3.
String name="javatpoint";
char ch=name.charAt(4);//returns the char value at the 4th index
System.out.println(ch);
−
Java is a high-level programming language originally developed by Sun
Microsystems and released in 1995. Java runs on a variety of platforms,
such as Windows, Mac OS, and the various versions of UNIX.
Java runs on a variety of platforms, such as Windows, Mac OS, and the
various versions of UNIX/Linux like HP-Unix, Sun Solaris, Redhat Linux,
Ubuntu, CentOS, etc.
Some features include Object Oriented, Platform Independent, Robust, Interpreted, Multi-threaded
When Java is compiled, it is not compiled into platform specific
machine, rather into platform independent byte code. This byte code is
distributed over the web and interpreted by virtual Machine (JVM) on
whichever platform it is being run.
Netbeans, Eclipse, etc.
Some Java keywords are import, super, finally, etc.
Object is a runtime entity and it’s state is stored in fields and
behavior is shown via methods. Methods operate on an object's internal
state and serve as the primary mechanism for object-to-object
communication.
A class is a blue print from which individual objects are created. A
class can contain fields and methods to describe the behavior of an
object.
Variables defined inside methods, constructors or blocks are called
local variables. The variable will be declared and initialized within
the method and it will be destroyed when the method has completed.
Default value of byte datatype is 0.
Default value of float and double datatype in different as compared to C/C++. For float its 0.0f and for double it’s 0.0d
This data type is used to save space in large arrays, mainly in place
of integers, since a byte is four times smaller than an int.
Java provides access modifiers to set access levels for classes,
variables, methods and constructors. A member has package or default
accessibility when no accessibility modifier is specified.
Postfix operators i.e () [] . is at the highest precedence.
Variables used in a switch statement can only be a string, enum, byte, short, int, or char.
This method is used to get the primitive data type of a certain String.
It is the process where one object acquires the properties of
another. With the use of inheritance the information is made manageable
in a hierarchical order.
Polymorphism is the ability of an object to take on many forms. The
most common use of polymorphism in OOP occurs when a parent class
reference is used to refer to a child class object.
It refers to the ability to make a class abstract in OOP. It helps to
reduce the complexity and also improves the maintainability of the
system.
These classes cannot be instantiated and are either partially
implemented or not at all implemented. This class contains one or more
abstract methods which are simply method declarations without a body.
If you want a class to contain a particular method but you want the
actual implementation of that method to be determined by child classes,
you can declare the method in the parent class as abstract.
It is the technique of making the fields in a class private and
providing access to the fields via public methods. If a field is
declared private, it cannot be accessed by anyone outside the class,
thereby hiding the fields within the class. Therefore encapsulation is
also referred to as data hiding.
The main benefit of encapsulation is the ability to modify our
implemented code without breaking the code of others who use our code.
With this Encapsulation gives maintainability, flexibility and
extensibility to our code.
Java Runtime Environment is an implementation of the Java Virtual
Machine which executes Java programs. It provides the minimum
requirements for executing a Java application;
JAR files is Java Archive fles and it aggregates many files into one.
It holds Java classes in a library. JAR files are built on ZIP file
format and have .jar file extension.
It improves the runtime performance of computer programs based on bytecode.
Object based programming languages follow all the features of OOPs
except Inheritance. JavaScript is an example of object based programming
languages.
If a class has multiple functions by same name but different parameters, it is known as Method Overloading.
If a subclass provides a specific implementation of a method that is
already provided by its parent class, it is known as Method Overriding.
Method overloading increases the readability of the program. Method
overriding provides the specific implementation of the method that is
already provided by its super class parameter must be different in case
of overloading, parameter must be same in case of overriding.
Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII
character set uses only 7 bits, it is usually represented as 8 bits.
UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16
uses 16-bit and larger bit patterns.
These are classes that allow primitive types to be accessed as objects. Example: Integer, Character, Double, Boolean etc.
AWT components are heavy-weight, whereas Swing components are
lightweight. Heavy weight components depend on the local windowing
toolkit. For example, java.awt.Button is a heavy weight component, when
it is running on the Java platform for Unix platform, it maps to a real
Motif button.
A break statement results in the termination of the statement to
which it applies (switch, for, do, or while). A continue statement is
used to end the current loop iteration and return control to the loop
statement.
The eight primitive types are byte, char, short, int, long, float, double, and boolean.
But, it is not forced to follow. So, it is known as convention not rule.
All the classes, interfaces, packages, methods and fields of java programming language are given according to java naming convention.
What is the purpose of this?
this is a keyword -it refers to the current object.
1.this: to invoke current class method
You may invoke the method of the current class by using the this keyword. If you don't use the this keyword, compiler automatically adds this keyword while invoking the method. Let's see the example
this.setVisible(true);
2. Used with JOptionPane.showMessageDialog(this,"to bring the frame in the center of the screen");
what is the purpose of extends keyword?
The extends keyword indicates that you are making a new class that derives from an existing class. The meaning of "extends" is to increase the functionality.
Explain what do you depict from this diagram?
What is Method Overloading?
If a class has multiple methods having same name but different in parameters, it is known as Method Overloading.
What is its advantage?
In the above diagram, byte can be promoted to short, int, long, float or double. The short datatype can be promoted to int,long,float or double. The char datatype can be promoted to int,long,float or double and so on.
What is final keyword?
final int speedlimit=90;//final variable
speedlimit=400;
Output:Compile Time Error
Explain encapsulation.
We can create a fully encapsulated class in java by making all the data members of the class private. Now we can use setter and getter methods to set and get the data in i
eg. JTextField.
What is the output?
1. String s1="javatpoint";
System.out.println(s1.substring(2,4));//returns va
System.out.println(s1.substring(2));//returns vatpoint
Advantage of OOPs over Procedure-oriented programming language
| 1)OOPs makes development and maintenance easier where as in Procedure-oriented programming language it is not easy to manage if code grows as project size grows. |
| 2)OOPs provides data hiding whereas in Procedure-oriented programming language a global data can be accessed from anywhere. |
| 3)OOPs provides ability to simulate real-world event much more effectively. We can provide the solution of real word problem if we are using the Object-Oriented Programming language. |
What is difference between object-oriented programming language and object-based programming language?
Object based programming language follows all the features of OOPs except Inheritance. JavaScript and VBScript are examples of object based programming languages.Java Naming conventions
Java naming convention is a rule to follow as you decide what to name your identifiers such as class, package, variable, constant, method etc.But, it is not forced to follow. So, it is known as convention not rule.
All the classes, interfaces, packages, methods and fields of java programming language are given according to java naming convention.
Advantage of naming conventions in java
By using standard Java naming conventions, you make your code easier to read for yourself and for other programmers. Readability of Java program is very important. It indicates that less time is spent to figure out what the code does.| Name | Convention |
|---|---|
| class name | should start with uppercase letter and be a noun e.g. String, Color, Button, System, Thread etc. |
| interface name | should start with uppercase letter and be an adjective e.g. Runnable, Remote, ActionListener etc. |
| method name | should start with lowercase letter and be a verb e.g. actionPerformed(), main(), print(), println() etc. |
| variable name | should start with lowercase letter e.g. firstName, orderNumber etc. |
What is the purpose of this?
this is a keyword -it refers to the current object.
1.this: to invoke current class method
You may invoke the method of the current class by using the this keyword. If you don't use the this keyword, compiler automatically adds this keyword while invoking the method. Let's see the example
this.setVisible(true);
2. Used with JOptionPane.showMessageDialog(this,"to bring the frame in the center of the screen");
what is the purpose of extends keyword?
The extends keyword indicates that you are making a new class that derives from an existing class. The meaning of "extends" is to increase the functionality.
Explain what do you depict from this diagram?
Java Inheritance Example
This indicates inheritance , Programmer is the subclass and Employee is the superclass. Relationship between two classes is Programmer IS-A Employee.It means that Programmer is a type of Employee.What is Method Overloading?
If a class has multiple methods having same name but different in parameters, it is known as Method Overloading.
What is its advantage?
Advantage of method overloading
Method overloading increases the readability of the program.What are the Different ways to overload the method
There are two ways to overload the method in java- By changing number of arguments
- By changing the data type
In the above diagram, byte can be promoted to short, int, long, float or double. The short datatype can be promoted to int,long,float or double. The char datatype can be promoted to int,long,float or double and so on.
What is final keyword?
Java final variable
If you make any variable as final, you cannot change the value of final variable(It will be constant).final int speedlimit=90;//final variable
speedlimit=400;
Output:Compile Time Error
Explain encapsulation.
Encapsulation in Java
Encapsulation in java is a process of wrapping code and data together into a single unit, for example capsule i.e. mixed of several medicines.We can create a fully encapsulated class in java by making all the data members of the class private. Now we can use setter and getter methods to set and get the data in i
eg. JTextField.
What is the output?
1. String s1="javatpoint";
System.out.println(s1.substring(2,4));//returns va
System.out.println(s1.substring(2));//returns vatpoint
2.
String s1="javatpoint";
String s2="python";
System.out.println("string length is: "+s1.length());//10 is the length of javatpoint string
System.out.println("string length is: "+s2.length());//6 is the length of python string
String s2="python";
System.out.println("string length is: "+s1.length());//10 is the length of javatpoint string
System.out.println("string length is: "+s2.length());//6 is the length of python string
3.
String name="javatpoint";
char ch=name.charAt(4);//returns the char value at the 4th index
System.out.println(ch);
4.
String s1="javatpoint";
String s2="javatpoint";
String s3="JAVATPOINT";
String s4="python";
System.out.println(s1.equals(s2));//true because content and case is same
System.out.println(s1.equals(s3));//false because case is not same
System.out.println(s1.equals(s4));//false because content is not same
String s2="javatpoint";
String s3="JAVATPOINT";
String s4="python";
System.out.println(s1.equals(s2));//true because content and case is same
System.out.println(s1.equals(s3));//false because case is not same
System.out.println(s1.equals(s4));//false because content is not same
5.
String s1="java string";
s1.concat("is immutable");
System.out.println(s1);
s1=s1.concat(" is immutable so assign it explicitly");
System.out.println(s1);
s1.concat("is immutable");
System.out.println(s1);
s1=s1.concat(" is immutable so assign it explicitly");
System.out.println(s1);
6.
String s1="javatpoint is a very good website";
String replaceString=s1.replace('a','e');//replaces all occurrences of 'a' to 'e'
System.out.println(replaceString);
}}
String replaceString=s1.replace('a','e');//replaces all occurrences of 'a' to 'e'
System.out.println(replaceString);
}}
jevetpoint is e very good website
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