What are runtime error in java

What are Runtime errors in Java

Some frequently encountered runtime errors are listed below: Input-output errors Infinite loop error Division by zero errors Logic Errors Out of range errors Undefined object error Factors that Cause Runtime Errors There are numerous factors that cause Runtime errors, among them the most commonly encountered causes are listed below: Dividing any numeric value by zero produces runtime errors. Types of runtime errors in Java Factors that Cause Runtime errors Examples of Runtime errors How to Handle Runtime Errors

What are Runtime errors in Java

In java, an unwanted event that terminates the program’s execution is known as an error. It occurs either because of syntactical issues or some other issues that can’t be detected at compile time. The errors that can’t be detected at compile-time and hence occur at the time of program execution are known as runtime errors while the errors with syntactical issues are referred to as compile-time errors.

This article presents a detailed overview of runtime errors in java and in this regard, we need to understand the following concepts:

• What are Runtime Errors in Java?
• Types of runtime errors in Java
• Factors that Cause Runtime errors
• Examples of Runtime errors
• How to Handle Runtime Errors

What are Runtime Errors in Java?

The errors that occur at the time of program execution are referred as runtime errors. These types of errors can’t be detected at the Compile time as there is nothing wrong with their syntax. So, we can say that the program that is syntactically correct still throws an error at the time of program execution is called a runtime error.

Types of Runtime Errors in Java

There are multiple types of runtime errors that we can face at the time of program execution. Some frequently encountered runtime errors are listed below:

• Input-output errors
• Infinite loop error
• Division by zero errors
• Logic Errors
• Out of range errors
• Undefined object error

Factors that Cause Runtime Errors

There are numerous factors that cause Runtime errors, among them the most commonly encountered causes are listed below:

• Dividing any numeric value by zero produces runtime errors.
• Accessing an array-out-of-bounds.
• Passing invalid data e.g. passing a numeric value to the non-numeric field.
• Passing invalid parameters/arguments to a method.
• Multiple processes trying to access the same resource at the same time.
• Trying to store an incompatible type value to a collection.
• Insufficient space/memory error in threads (OutOfMemoryError)

Examples of Runtime Errors

Let’s understand the concept of runtime errors with the help of examples.

Example

In this example, we have an array of size three:

public class RuntimeErrorsExample <
public static void main ( String [ ] args ) <
int ary [ ] = < 4 , 6 , 2 >;
System . out . println ( «Result: » + ary [ 3 ] ) ;
>
>

The array’s length is three and we knew that the array’s indexing starts from zero. So, specifying ary[3] means we are trying to access the fourth element of the array. Syntactically, nothing wrong with it so, we didn’t face any error at compile time. However, the JVM will throw the error at runtime:

From the above snippet, we observe that an error occurs at run time when we try to access the out-of-range index.

For the clarity of concept let’s consider another example:

Example

This time we have a string assigned with a “null” value and we will try to find the length of the string:

public class RuntimeErrorsExample <
public static void main ( String [ ] args ) <
String str = null ;
System . out . println ( str. length ( ) ) ;
>
>

Following will be the output for the above code snippet:

When we run the program, we encounter a NullPointerException because the string is null.

So, how to handle such runtime errors? Does java provide a solution to deal with such runtime errors? Of course, Java does.

How to Handle Runtime Errors

In java, Runtime errors can be solved with the help of try-catch statements, and to do so, we have to put the code that can throw a runtime error in the try-catch statements.

Example

Let’s consider the below code snippet to understand how to solve runtime errors using try-catch statements in java:

public class RuntimeErrorsExample <
public static void main ( String [ ] args ) <
try <
int number1 = 110 , number2 = 0 ;
System . out . println ( «Outcome: » + number1 / number2 ) ;
> catch ( ArithmeticException excep ) <
System . out . println ( «Numeric values can’t be divided by 0» ) ;
>
>

Now we surrounded the code within the try-catch statements that can throw the error:

Now this time instead of throwing the error, JVM shows the message that we specified within the catch block.

Conclusion

In Java, the programs that are syntactically correct but still throw some errors at the time of program execution are known as runtime errors. These errors occur because of different reasons such as division by zero, Accessing an array out of bounds, passing invalid data e.g. passing a numeric value to the non-numeric field, etc. These types of errors can be handled by surrounding the try-catch block around the code that can throw the runtime errors. This write-up explains different aspects of runtime errors for example what are runtime errors, their types, causes, and how to fix these errors in java.

Types of Errors in Java with Examples, Compile Time Errors are those errors which prevent the code from running because of an incorrect syntax such as a missing semicolon at the end

Top 10 Java Compile Time Errors (And How to Fix Them)

Read more: https://www.theserverside.com/tutorial/The-most-common-compile-time-errors-in Duration: 11:29

Java Tutorials : Compile Time vs Runtime Errors #45

Compile Time Vs Run Time Error in Java

Compile Time Vs Run Time Error in Java. 8,388 views8.3K views. Sep 3, 2015. 57. Dislike
Duration: 0:43

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

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

import java.io.File; import java.io.FileReader; public class FilenotFound_Demo < public static void main(String args[]) < File file = new File("E://file.txt"); FileReader fr = new FileReader(file); >>

Output

C:\>javac FilenotFound_Demo.java FilenotFound_Demo.java:8: error: unreported exception FileNotFoundException; must be caught or declared to be thrown FileReader fr = new FileReader(file); ^ 1 error

Custom exception class throws compile-time error, You need extends java.lang. · Using java programming conventions, packages use entirely lower case letters. · Adding a couple of more tips here: 1

Java Terminology: Why compile-time error and not compile-time exception?

This may sound awkward .
But I didn’t understand it.

Why do we have compile-time error and not compile-time exception in java ?

I mean to say that we never say compile-time exception.
We tend to say it as compile-time error .

Is there any specific reason for the same ??
Any suggestions are welcomed.

The reason for this is that an exception is something thrown during execution of a program. Java has a specific type for this, the Exception class.

At compile time, your code is not executing, so it cannot throw an exception. Indeed, it is proper execution of the compiler to find errors in your code — certainly not an exception case!

Exception in java is really different than compile error. We don’t have the term compile time exception. Because exception is something happens that you don’t expect it to happen. We only have checked and unchecked exception. With checked exception, in compile time , the compiler will force you to catch it, but it is not an error . Don’t catch it, you can not compile the program but it is not a compile error.

An error indicates that there is a problem with the program. An exception is a specific construct that interrupts the control flow of the program, and unwinds the stack, capturing information about the state of the stack so that it can be reported.

An exception can be used to indicate an error, but not always. For example:

void startOperation() < try < while (someComplexOperationIsOnGoing()) < checkRestart(); >> catch (RestartException re) < startOperation(); >> void checkRestart() < if (shouldRestart()) < throw new RestartException(); >> 

This incomplete code sample is meant to show a case where an exception is not an error. This is not always best practice; but it is used in some cases where the intent is to interrupt the control flow deep in the program (such as redirecting the page in a web framework, when responding to an HTTP request) and return control to a higher-up level of the stack. The term exception refers to the mechanism which interrupts the program.

In java, there is an Exception class which encapsulates this behavior. The Error class also interrupts the control flow in the same way as an Exception; but it is reserved only for serious, unrecoverable problems that happen at runtime. It is used, for example, when the JVM runs out of memory and can’t create new objects.

Exception is something more of an unexpected flow that can be handled. Compile time error is more like invalid code..so code doesn’t even compile.. Hence term «error» since it denotes more serious problem which has to be fixed.

Why do I get a compile-time error when calling a subclass method using superclass reference?

I know polymorphism happens in the case of method overriding. But I am a little confused about the below.

class A < public void hi() < System.out.println("A "+this.getClass().getName()); >> class B extends A < public void bye() < System.out.println("B "+this.getClass().getName()); >> class Ideone < public static void main (String[] args) throws java.lang.Exception < A a = new B(); a.hi(); a.bye(); >> 

Main.java:35: error: cannot find symbol a.bye(); ^ symbol: method bye() location: variable a of type A 1 error 

Why does this give a compile time error?

In a = new B() , the B class object is created at runtime, so a ‘s a reference variable pointing to an object of type B .

Now if we call B ‘s class method bye() , why it is a compiler time error?

The a variable may contain in run-time an instance of class A or any sub-class of A . Therefore, you can only call methods of class A for that variable.

The compiler only cares about the compile-time type of the variable when it determines which method calls are valid.

The declared type of the variable a is A. The compiler doesn’t know (and shouldn’t know) what its concrete type at runtime is B. All it knows is that it’s a A, and that there is no bye() method in A.

is to clearly say that a is a A, and could have any concrete type, as long as the conrete type extends A. You must be able, if you find a better implementation of A later, to just change that line to

A a = new BetterImplementation();

and have the code compile.

Assigning the new B instance to a reference of type A is like making it wear the only-see-methods-defined-at-A glasses. That is you get the interface described at A . And even though that instance has an implementation for bye , you can only access hi .

An easy way to understand this is that A a might be actually pointing to the object of B, but during compile time the compiler doesn’t know that.

The compiler only checks the reference i.e. ‘a’ and sees if its class , i.e. ‘A’ has the method that its reference ‘a’ is trying to call.

In your case, the reference ‘a’ does not have a method called bye() so according to the compiler such a call cannot be made and that is why you see that error.

Runtime vs. Compile Time | Baeldung on Computer Science, We use high-level programming languages such as Java to write a program. The instructions or source code written using high-level language is

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