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So just got into the basics of try-catch statements in Java and I'm still a bit confused on some differences within the syntax.

Here is the code I'm trying to analyze and understand. What's the difference between using try then catch(Exception e) as compared to saying just throws or throw new?

From my understanding, a try and catch is basically a way to handle the error by outputting a message or passing to another method. However, I think I'm stuck on the syntax aspect of it.

Any constructive comments or simple examples clarifying this concept as well as whats going on with the sample code from my book would be appreciated.

/* Invalid radius class that contains error code */
public class InvalidRadiusException extends Exception {
     private double radius;

/** Construct an exception */
public InvalidRadiusException(double radius) {
       super("Invalid radius " + radius);
       this.radius = radius;
}

/** Return the radius */
public double getRadius() {
    return radius;
 }
}


public class CircleWithException {
/** The radius of the circle */

private double radius;

/** The number of the objects created */
private static int numberOfObjects = 0;

/** Construct a circle with radius 1 */
public CircleWithException() throws InvalidRadiusException {
       this(1.0);
  }

/** Construct a circle with a specified radius */
public CircleWithException(double newRadius) throws InvalidRadiusException {
          setRadius(newRadius);
          numberOfObjects++;
}

/** Return radius */
public double getRadius() {
     return radius;
}

/** Set a new radius */
public void setRadius(double newRadius)
    throws InvalidRadiusException {
if (newRadius >= 0)
  radius =  newRadius;
else
  throw new InvalidRadiusException(newRadius);
}

/** Return numberOfObjects */
public static int getNumberOfObjects() {
      return numberOfObjects;
}

/** Return the area of this circle */
public double findArea() {
    return radius * radius * 3.14159;
 }
}
Explanation

From the Java documentation:

[The try block] contains one or more legal lines of code that could throw an exception. (The catch and finally blocks are explained in the next two subsections.)

An exception is a special kind of object. When you write new Exception(), you are creating a new exception object. When you write throw new Exception() you are creating a new error, and then throwing it to the nearest try-catch block, aborting the rest of your code.

When you throw an exception, it gets caught by the try-catch block that it's nested in (inside of). That is, assuming the proper catch block for that exception is registered. If the code is not wrapped in a try-catch block, the program with automatically shut down as soon as an error is thrown. Use a try-catch around any code or method that can throw an error, especially because of user input (within reason).

Some exceptions have to be caught, others are optional to catch. (checked vs. unchecked).

When you add throws to a method signature, you are announcing to other methods that if they call that method, it has the potential to throw a checked exception (it is not necessary for unchecked). Notice how it's throws not throw. It's not doing an action, it's describing that it sometimes does an action.

You use this functionality when you don't want to catch the error inside that method, but want to allow the method's that call your method to catch the error themselves.

Exceptions are a way to make your program respond coherently to unexpected or invalid situations and are especially useful when user input is required, though it's also useful in other situations such as File input/output.

Examples
public CircleWithException() throws InvalidRadiusException {
       this(1.0);
}

Here, the CircleWithException() has the potential to throw an InvalidRadiusException (presumably, the this(1.0) sometimes throws an InvalidRadiusException.)

The code calling this method should have:

try {
    new CircleWithException(); // This calls the method above
} catch (InvalidRadiusException e) { // The object "e" is the exception object that was thrown.
    // this is where you handle it if an error occurs
}

As I said before, an Exception is just a specific type of object that extends Exception

/* Invalid radius class that contains error code */
public class InvalidRadiusException extends Exception {
     private double radius;

/** Construct an exception */
public InvalidRadiusException(double radius) {
       super("Invalid radius " + radius);
       this.radius = radius;
}

/** Return the radius */
public double getRadius() {
    return radius;
 }
}

The above code defines a new type of Exception specific to your program/application. There are many predefined exceptions in the Java Standard Library, but often you need to create your own.

To throw this exception, you first create an InvalidRadiusException object and then throw it:

throw new InvalidRadiusException(1.0);

Try Catch in Java - Exception handling, You can catch different exceptions in different catch blocks. When an exception occurs in try block, the corresponding catch block that handles that particular exception executes. For example if an arithmetic exception occurs in try block then the statements enclosed in catch block for arithmetic exception executes. Java try-catch block Java try block. Java try block is used to enclose the code that might throw an exception. It must be used within the Java catch block. Java catch block is used to handle the Exception by declaring the type of exception within the Problem without exception handling. Let's

You can declare a method to throw an exception if you can't (or it's not convinient) to handle the exception inside the method.

In your case, you are calling the method setRadius inside the constructor. If you think that is convinient to handle the exception (that is thrown by setRadius) inside the constructor, you can use a try-catch clause:

public CircleWithException(double newRadius) throws InvalidRadiusException {
    try {
        setRadius(newRadius);
        numberOfObjects++;
    } catch (InvalidRadiusException e) {
        setRadius(0); // for example
    }
}

The catch block contains what you want to do if an exception were thrown. In this case, I'm setting the radius to 0, but you can change this.

Remember that it depends in your classes implementation and how you want them to work. If you don't want the constructor to handle this exception, you can throw it (as you are already doing) and handle it in other methods.

Java try-catch, Java try block is used to enclose the code that might throw an exception. It must be used try block only. You can use multiple catch block with a single try block. Try Catch in Java – Exception handling Try block. The try block contains set of statements where an exception can occur. A try block is always followed by a Catch block. A catch block is where you handle the exceptions, this block must follow the try block. A single try block Example: try

Java try-catch Examples, A try statement is used to catch exceptions that might be thrown as your program executes. You should use a try statement whenever you use a statement that� Java try-catch block is used to handle exceptions in the program. The code in the try block is executed and if any exception occurs, catch block is used to process them. If the catch block is not able to handle the exception, it’s thrown back to the caller program.

There are two types of exceptions

1) Unchecked. These are defined by the Error and RuntimeException classes and all of their subclasses. Java does not force you to handle these exception in any way.

2) Checked. These are defined be the Throwable class and all of its subclasses that do not fall into the category defined in (1). Java forces you to handle these exceptions with a try/catch. If you call a method that can throw such an exception (defined with the throws keyword) outside of a try block your code will not compile.

throws : This is a way of declaring that a method can potentially throw an exception that must be caught with a try/catch. For example

public void doSomething() throws MyException { ... }

is a declaration of a method that can potentially throw an instance of MyException.

try/catch/finally : This is a way of handling exceptions that may be produced by some sort of code. The cody you are trying to run goes in the try block, the error handling code goes into the catch block. The optional finally block is something that will be executed regardless of whether or not an exception is thrown. In fact the finally block will be called even if you do a return inside your try or your catch. For example

try {
    doSomething();
} catch (MyException exception) {
    exception.printStackTrace();
}

or an example of using finally :

MyResource myResource = getMyResource();
try {
    myResource.open();
    doStuffWithMyResource(myResource);
} catch (Exception exception) {
    exception.printStackTrace();
} finally {
    if (myResource.isOpen()) {
        myResource.close();
    }
}

Try Statements in Java, Control flow in try-catch clause OR try-catch-finally clause. Case 1: Exception occurs in try block and handled in catch block; Case 2: to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your� try / catch / finally : This is a way of handling exceptions that may be produced by some sort of code. The cody you are trying to run goes in the try block, the error handling code goes into the catch block. The optional finally block is something that will be executed regardless of whether or not an exception is thrown.

Flow control in try catch finally in Java, This is how to use write a try catch statement in java! ✅Hopefully, what I've taught you will Duration: 11:05 Posted: May 2, 2019 The trycatch block is used in Java to handle exceptions gracefully. The code within the try block is executed, and if an exception is raised, the code within the relevant catch block is executed. In addition, the finally statement is used to execute code after the trycatch block has executed, even if no exception was raised.

Try Catch Java Tutorial, try { } catch (ExceptionType name) { } catch (ExceptionType name) { } a decision, or propagate the error up to a higher-level handler using chained exceptions,� Video 9: A first look at the syntax and use cases for a try/catch/finally. Subscribe for more! Check out other content on TikTok, Instagram, and Facebook: @redneckprogrammer Twitter

The catch Blocks (The Java™ Tutorials > Essential Classes , Learn exception handling, try catch, exception hierarchy and finally block with Run the program using command, java JavaException. Java provides an inbuilt exceptional handling. The normal code goes into a TRY block. The exception handling code goes into the CATCH block In our example, TRY block will contain the code to connect to the server.

Comments
  • Have you read this?
  • correct. However, its when you throw something, catch it, then pass it on to more methods, use it in if-else statements or simply say some method name + throws which is what gets me.
  • @Andy897 try chat.stackexchange.com
  • @Andy897 we are allowed to further continue this discussion in chat i believe.
  • @MarounMaroun your analogy makes no sense.
  • when you say throws in your first line, r u declaring that if it throws InvalidRadiusException or that it might throw it? In which case it is there as a security precaution?
  • Some examples of what I wanted to say, are your constructors. They both throw the exception InvalidRadiusException. But note that they don't do it "directly". They call a method (which in fact, has the throw new InvalidRadiusException; line) but don't handle it.