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Object Oriented Programming Articles
Page 588 of 588
What is the difference between compile time errors and run time errors in Java?
Compile time errors are syntactical errors in the code which hinders it from being compiled. Example public class Test{ public static void main(String args[]){ System.out.println("Hello") } } Output C:\Sample>Javac Test.java Test.java:3: error: ';' expected System.out.println("Hello") An exception (or exceptional event) is a problem that arises during the execution of a program. When an Exception occurs the normal flow of the program is disrupted and the program/Application terminates abnormally, which is not recommended, therefore, these exceptions are to be handled. Example ...
Read MoreIs it necessary that a try block should be followed by a catch block in Java?
Not necessarily catch, a try must be followed by either catch or finally block. Example import java.io.File; public class Test{ public static void main(String args[]){ System.out.println("Hello"); try{ File file = new File("data"); } } } Output C:\Sample>Javac Test.java Test.java:5: error: 'try' without 'catch', 'finally' or resource declarations try{ ^ 1 error
Read MoreWhat are checked exceptions in Java?
A checked exception is an exception that occurs at the time of compilation, these are also called as compile time exceptions. These exceptions cannot simply be ignored at the time of compilation; the programmer should take care of (handle) these exceptions. if you use FileReader class in your program to read data from a file, if the file specified in its constructor doesn't exist, then a FileNotFoundException occurs, and the compiler prompts the programmer to handle the exception. Example import java.io.File; import java.io.FileReader; public class FilenotFound_Demo { public static void main(String args[]) { ...
Read MoreWhat are number format exceptions in Java?
This Exception happens once you associated convert a string variable in an incorrect format to a whole number (numeric format) that's not compatible with one another. Example public class Test { public static void main(String[] args) { int data = Integer.parseInt("hello"); } } Output Exception in thread "main" java.lang.NumberFormatException: For input string: "hello" at java.lang.NumberFormatException.forInputString(Unknown Source) at java.lang.Integer.parseInt(Unknown Source) at java.lang.Integer.parseInt(Unknown Source) at a6.dateAndTime.Test.main(Test.java:5)
Read MoreWhat is the difference between System.out, System.in and System.err streams in Java?
All the programming languages provide support for standard I/O where the user's program can take input from a keyboard and then produce an output on the computer screen. Similarly, Java provides the following three standard streams:Standard Input: This is used to feed the data to user's program and usually a keyboard is used as a standard input stream and represented as System.in.Standard Output: This is used to output the data produced by the user's program and usually a computer screen is used for standard output stream and represented as System.out.Standard Error: This is used to output the error data produced ...
Read MoreHow can dead thread be restarted in Java?
A thread goes through various stages in its lifecycle. For example, a thread is born, started, runs, and then dies. New − A new thread begins its life cycle in the new state. It remains in this state until the program starts the thread. It is also referred to as a born thread. Runnable − After a newly born thread is started, the thread becomes runnable. A thread in this state is considered to be executing its task. Waiting − Sometimes, a thread transitions to the waiting state while the thread waits for another thread to perform a task. ...
Read MoreWhat is the Thread class in Java?
The java.lang.Thread class is a thread of execution in a program. The Java Virtual Machine allows an application to have multiple threads of execution running concurrently. Following are the important points about Thread −Every thread has a priority. Threads with higher priority are executed in preference to threads with lower priority.Each thread may or may not also be marked as a daemon.There are two ways to create a new thread of execution.One is to declare a class to be a subclass of Thread.Another way to create a thread is to declare a class that implements the Runnable interface.
Read MoreCan constructors be inherited in Java?
No, constructors cannot be inherited in Java. In inheritance sub class inherits the members of a super class except constructors. In other words, constructors cannot be inherited in Java therefore, there is no need to write final before constructors. Example public interface InterfaceTest { public InterfaceTest(){ } public abstract void display(); public abstract void show(); } Still, if you try to write constructors in an interface it will generate a compile time error. Error C:\Sample>javac InterfaceTest.java InterfaceTest.java:2: error: expected InterfaceTest(){ ^ 1 error C:\Sample>
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