Why Compiler Compels Only Checked Exception To Be Put In Try Catch Clause Not RuntimeException
Mar 11, 2014
what is the use of checked exception.I know unchecked exception or Runtime exception are thrown by jvm whenever programmer makes any mistake in logic and current thread is terminated.But checked Exception are checked at compile time so that compiler compels programmer to put risky methods in try catch clause. And this checked Exception are caused due to problem in IO operation or any such operation which the programmer can't control.Programmer can't do anything to avoid this checked exception but can catch this exception.
Now the question is Why compiler compels checked exception to be put in try catch clause but doesn't complain anything in case of Runtime Exception???
I was giving a quick skim to some tutorials on the internet where I have found the exception that is handled is also declared in the throws clause of the method wrapping the try-catch block. For a code representation consider the following:
public void methodName() throws IOException { try { ... } catch (IOException ex) { .... TODO handle exception }
I know checked exception need to be checked at compile time and runtime exception need not be checked at compile time.
My question is not related to the definition.
The question is on what basis have they selected that FileNotFound exception is a checked exception and NullPointerException is an unchecked exception? Is it the random wish of the creator or is there reason behind why something is selected as checked exception and something as unchecked?
I came across a code where the exceptions can be thrown from catch and finally block too. I never gave a thought on what scenarios that can be required. Some practical examples when/where it can be required to throw the exception from catch and finally blocks.
I want to write classes with methods that perform JDBC operations that throw SQL exceptions. For many of the methods, I'd ideally like to be able to have them catch exceptions and just send them to a standard Logging system "IF" the code that calls the methods is not going to catch the same exception. However, I'd like the "option" to have code that calls these methods catch the same errors if I want to but not "Require" the calling routines to catch them.... so I don't want to declare the methods with a "throws" that would require all calling code to Try/catch.
For some background, the logic behind what I'm looking to do is that there will be lots of places where these classes and their methods may be used where the code is basically "throw away" scripting code where just having error logs generated is more than sufficient. However there are also places I want to use the same classes/methods that I would want to handle the exception differently. So, for at least half the places I want to use these methods, there's no good reason to require cluttering the calling code with Try/catch, but when I DO want to handle the exceptions, I'd like them to get passed up to the calling routine so I can handle them in a way that is appropriate for the calling routine. Does that make sense?
I guess I'm kind of looking for is the ability to "override" the catch of a called method "IF" I want to but to treat the method as though it doesn't throw any exception "IF" I don't want to override the called routines catch logic.
The requirement is to write a rectangle class and a test class, which include try-catch blocks and exception handling. Exceptions, involving try, catch, throw, throws, and finally commands,how to write a code about basic things, but in the test class, it gives me specific width and height so that i dont konw how to write a try-catch blocks an exception handling in this test class.There is my two classes, they are separated.
public class Rectangle { double width ; double height ; Rectangle(){ width = 1; height = 1;
If I put the highlighted text in try/catch block it is throwing NullPointerException , if I am using command line arguments then also it is showing the same exception.
java 7 feature (Multicatch and final rethrow ).. how to print user defined message in catch block with respect to multiple exceptions in single catch block...
Ex: }catch (IOException | SQLException ex) { System.out.println("Exception thrown"); /** * i want like this, if IOException is thrown then System.out.println("File not Found"); * if SQLException is thrown then System.out.println("DataBase Error"); */ }
There is a method taken from a class with several try and catch blocks. If you think it is possible, add one more catch block to the code to catch all possible exceptions, otherwise say 'Not possible' with your reason.
Check out the following basic code (assume that dog has a method called bark):
Dog d = new Dog(); Object o = d;
o.bark(); // error
But why? Isn't o just a pointer to a memory address which has the dog object? If so, why can't the compiler see that the object has a method called bark? Or, to ask the question another way, why is Java designed to check the object reference to see if the method exists instead of the object itself?
I am using a IN clause in Oracle DB to pass a collection of custId to retrieve the customer details. If it was 10 or 50 custId's as a collection in IN clause it works fine. But if the collection grows bigger to 500 or 1000 then it is pretty slow to load the JSP page with the customer details.
Here is the query:-
select CustName, CustAge, CustCity, CustPin from CUSTOMER where custId IN (....)
The list of custId that is passed through Hibernate query.setParameterList()
How to optimize this query to make sure it displays the customer details faster even if the collection of elements which we pass is huge?
I have a mySql table of PROJECTS, which I am displaying as a list in the index.xhtml. The projectid column contains hyperlinks. When they're clicked I would like the specific projectid row selected to be passed as the query argument into another jsf file (ListProjects.xhtml) which displays all the project values referring to the projectid selected in the index.xhtml. The named query is:
@NamedQuery(name = "Projects.findByProjectid", query = "SELECT p FROM Projects p WHERE p.projectid = :projectid") index.xhtml <?xml version='1.0' encoding='UTF-8' ?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"
[Code] ....
I get the following stack trace. How to correctly pass the hyperlink parameters.
org.jboss.weld.exceptions.WeldException: WELD-000049 Unable to invoke public void com.manaar.beans.SelProjectMgtBean.init() on com.manaar.beans.SelProjectMgtBean@681859ae at org.jboss.weld.injection.producer.DefaultLifecycleCallbackInvoker.invokeMethods(DefaultLifecycleCallbackInvoker.java:91)
class Animal { void makeNoise() {System.out.println("generic noise"); } } class Dog extends Animal { void makeNoise() {System.out.println("bark"); } void playDead() { System.out.println("roll over"); }
[Code] .....
The book states that the above code will compile if there is a downcast in the line 14 . But there is a compiler error saying playDead method is not defined for type animal even after downcasting.
Running a java source code through an online java compiler (in which you will just pass the the source code using a http request, then the compiler will return the output/error of the source code automatically)?.
I am working in software testing, specifically automatic test cases generation. Among the existing forms of test cases, my focus is on the test cases that are composed of sequences of events such as _.event1.event2 eventx()
However, the events can be classified into: sensitive and insensitive. The latter does not affect the system's states, and hence, it can be ignored; while the former affects the states. Anyhow, the sensitive events in the test cases may lead to states explosion and there is a need to prevent that. Therefore, some techniques suggest using one variable to present states and group all similar states together such as using len variable in circular queue. Relatively, the states can be represented by using specific drawings such FSM.
For example, the test cases for circular queue may look like:
len=1, rear=0, front=0 and dataQ[0]=0 len=0, rear=0, front=1 and dataQ={0} len=1, rear=1, front=1 and dataQ[1]=1
len=1, rear=0, front=0 and dataQ[0]=0 len=2, rear=1, front=0 and dataQ[1]=1 len=1, rear=1, front=1 and dataQ={1,0}
As can be seen, every addition/deletion produces a new state. A state is composed of 4 variables: len, rear, front and dataQ. The 1st three variables are integers while the dataQ is an integer array. Nonetheless, the states produced by different test cases can be identical which wastes effort and time. So, there is a need to optimize these states. The search techniques were suggested where the problem can be represented as a search problem and the technique is applied. If we consider Len as a state, then we will have: len=0; 0QSize. However, this does not represent the state but it suits for classifying the states into groups.
In terms of states representation, State Machine/Map Compiler (SMC) was suggested as a modeling mechanism that takes the state machines (i.e. FSM) drawing and generates the code in any preferred language. In SMC, the FSM is represented in a specific syntax (state---transition----next state) and saved in a file (.sm). This file will be compiled by SMC to generate a context class which includes definitions of states, transitions and actions in FSM but still need to be triggered by another class. This class has to call the transitions that modifies the state.
We had created that class and implemented all the methods with their transitions. However, the FSM used was based on 1 variable only (i.e. len). Besides, we are still looking for the SMC results as they will be the input for any search technique to be applied. Supposedly, the states generated by SMC can be used directly in the search technique but this is still questionable.
I have started to learn JAVA and was referring Head First JAVA book. I have 3 separate .java files - GuessGame.java , Player.java, GameLauncher.java I have successfully compiled GuessGame.java & Player.java
But I am getting an error when I am compiling GameLauncher.java.
public class Main { private static void foo(Integer a) { System.out.println("Integer"); } private static void foo(long a) { System.out.println("long");
[Code] ....
This code prints long. Why is that? How did compiler decided that it likes long version of foo() method the most. If I had to guess I'd pick int... or possibly Integer as they are most similiar to what was passed. But why long?
I'm a beginner fiddling around classes in Java. I noticed on this particular code, Eclipse will give me an error and suggest I put the static keyword in front of the variable.
public class test { //the following line is where Eclipse puts the static keyword static FileAccess hello = new FileAccess("D:" + '\', ".mp3"); public static void main(String[] args) { for (int i = 0; i < hello.getTotalNumberOfFiles(); i++) {
[Code] .....
The FileAccess class is just a class I made while trying to retrieve filenames from my hard drive.
As far as I can tell, it works correctly after I put the static keyword there. I just want to know why it is required in this particular code, considering it didn't need to do that when I made a simpler class while I was getting my feet wet at creating classes in Java.
public void init(Board board) { JPanel Panel = new JPanel(); Panel.setLayout(new GridLayout(board.getWidth(), board.getHeight())); getContentPane().add(Panel, BorderLayout.CENTER); Panel.setBorder(new LineBorder(Color.BLACK)); // it does not work also
[code]....
I have a JFrame. I added two JPanels to the JFrame. The first one is GridLayout and it should be situated at CENTER. Another one is bottomPanel, and that one should be situated at SOUTH.I would like to add two new JPanels(kit and another one) to the bottomPanel.Compiler does not show any warning or errors.The problem is, that bottomPanel situates at NORTH, not at SOUTH. kit situates at CENTER of bottomPanel, not at WEST.
I was trying to execute the following codes, but the something that I don't undestand was happen. The program was compiled differently according to ouput picture of the program in my java book. Furthermore, then I tried to compile the program in eclipse and NetBeans. I saw that all of output are different each other.
package finallyblock; public class FinallyBlock { public static void main(String[] args) { try{ throwException(); } catch(Exception exception){ System.err.println("Exception handled in main");
