How can I print "Error" while the JTextfield is empty
save.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e)
{
String sn =jX1.getText();
if (sn==null){
System.out.println("Error");
System.out.println("T");
}
Thanks
Try using a fail-safe method. Also Expanding on the comments, you should be logging data, in a better format. Java hosts a huge array of different way to log certain data. look here
As for your error handling, try-catch-finally. This isn't tested code. Let me know if you run into any issues, documentation on try-catch and other statements here or here
public static void main(String[] args) {
while (String sn == null)
try {
String sn = JX1.getText();
} catch (Exception ex) {
System.out.println("Exception thrown!");
} finally {
if (sn != null) {
System.out.println("Closing PrintWriter");
sn.close();
} else {
System.out.println("PrintWriter not open");
}
}
Related
I thought I would do a little digging about cataching exceptions.
According to this question (C++ catching all exceptions) one of the answers states:
[catch(...)] will catch all C++ exceptions, but it should be considered bad design.
At the moment I have used this approach:
CPTSDatabase::~CPTSDatabase()
{
try
{
CloseDatabase();
}
catch(...)
{
}
}
void CPTSDatabase::CloseDatabase()
{
if (m_dbDatabase.IsOpen())
m_dbDatabase.Close();
}
I thought that this was the correct way because when I trace into CDatabase::Close() it does something similar:
// Disconnect connection
void CDatabase::Close()
{
ASSERT_VALID(this);
// Close any open recordsets
AfxLockGlobals(CRIT_ODBC);
TRY
{
while (!m_listRecordsets.IsEmpty())
{
CRecordset* pSet = (CRecordset*)m_listRecordsets.GetHead();
pSet->Close(); // will implicitly remove from list
pSet->m_pDatabase = NULL;
}
}
CATCH_ALL(e)
{
AfxUnlockGlobals(CRIT_ODBC);
THROW_LAST();
}
END_CATCH_ALL
AfxUnlockGlobals(CRIT_ODBC);
if (m_hdbc != SQL_NULL_HDBC)
{
RETCODE nRetCode;
AFX_SQL_SYNC(::SQLDisconnect(m_hdbc));
AFX_SQL_SYNC(::SQLFreeConnect(m_hdbc));
m_hdbc = SQL_NULL_HDBC;
_AFX_DB_STATE* pDbState = _afxDbState;
AfxLockGlobals(CRIT_ODBC);
ASSERT(pDbState->m_nAllocatedConnections != 0);
pDbState->m_nAllocatedConnections--;
AfxUnlockGlobals(CRIT_ODBC);
}
}
And the CDatabase::Close documentation does not even state anything about exceptions being thrown.
The linked answer does state:
You can use c++11's new current_exception mechanism.
It is not clear if we can use this approach given the CDatabase class we are using.
Since CDatabase::Close() is using THROW_LAST to throw CDBException, you have to use catch (CDBException* e). Even if you are not handling it, you still have to Delete the error. You might as well do this when CDatabase methods are called directly:
void CPTSDatabase::CloseDatabase()
{
try
{
if (m_dbDatabase.IsOpen())
m_dbDatabase.Close();
}
catch (CDBException* e)
{
//TRACE(L"DB error: " + e->m_strError);
e->Delete();
}
}
Or use
CPTSDatabase::~CPTSDatabase()
{
try { CloseDatabase(); }
catch (CDBException* e) { e->Delete(); }
catch(...) {}
}
Because in this code it's not clear where the exceptions are coming from. catch(...) {} will deal with other exceptions. In general catch(...) {} is not recommended because it doesn't give useful information, it just says "something went wrong..."
Use Standard Library exceptions only if you are adding throw in your own code, or when using std functions. Example:
try { std::stoi("wrong argument"); }
catch (const std::exception& e) { TRACE("%s\n", e.what()); }
try { throw 123; }
catch (int i) { TRACE("%d\n", i); }
I am working on two apps, in one of my app "A" i applied retrofit 2.
This was the method i used to retrieve data.
But here in on Response the data retrieved in response body can be set to activity variables and can be used outside this method without getting null values.
public void fetch_information() {
ApiInterface = ApiClient.getApiClient().create(Api.class);
Call<List<City>> call = ApiInterface.GetCities();
call.enqueue(new Callback<List<City>>() {
#Override
public void onResponse(Call<List<City>> call, Response<List<City>> response) {
citylist = new ArrayList<City>();
citylist = response.body();
cities = new String[citylist.size()];
citiesid = new String[citylist.size()];
for (int i = 0; i < citylist.size(); i++) {
cities[i] = citylist.get(i).getCityName();
citiesid[i] = citylist.get(i).getCityId();
}
city_adapter = new ArrayAdapter<String>(Pay_Payment_X.this, android.R.layout.simple_list_item_1, cities);
city_adapter.setDropDownViewResource(R.layout.spinner_dropdown_layout);
City_Spinner.setAdapter(city_adapter);
}
#Override
public void onFailure(Call<List<City>> call, Throwable t) {
Toast.makeText(getApplicationContext(), t.getMessage(), Toast.LENGTH_SHORT).show();
}
});
}
after applying this method and on debugging this method i will retain values of varaibles "cities" and "citiesid"out side onResponse.
But applying retrofit 2 similarly on another app "B", i did the same thing for retrieving data on different URL.
ApiUtil.getServiceClass().getAllPost().enqueue(new Callback<List<ApiObject>>() {
#Override
public void onResponse(Call<List<ApiObject>> call, Response<List<ApiObject>> response) {
if (response.isSuccessful()) {
List<ApiObject> postList = response.body();
try {
for (int i = 0; i < postList.size(); i++) {
String Name = postList.get(i).getGamesName();
mGamesName.add(Name);
}
} catch (Exception e) {
}
Log.d(TAG, "Returned count " + postList.size());
NewAdapter adapter = new NewAdapter(getApplicationContext(), postList);
recyclerView.setAdapter(adapter);
}
}
#Override
public void onFailure(Call<List<ApiObject>> call, Throwable t) {
//showErrorMessage();
Log.d(TAG, "error loading from API");
}
});
the data is retrievable inside onResponse but outside it shows null.
So here variables are not retaining values.
Why is this happening?
the only thing came to mind is retrieving data can take time while your code lines are being read and finding null values as data has not been received yet.
Also to mention in app "A" the data retrieved is huge but in app "B" only 3 objects with string values.But still in app"A" data is retrievable.
In app 2 did this for resolving my issue.
public void doRequest( final ApiCallback callback){
ApiUtil.getServiceClass().getAllPost().enqueue(new Callback<List<ApiObject>>() {
#Override
public void onResponse(Call<List<ApiObject>> call, Response<List<ApiObject>> response) {
if (response.isSuccessful()) {
List<ApiObject> postList = response.body();
callback.onSuccess(postList);
// apobject =response.body();
if(response.isSuccessful()) {
try {
for (int i = 0; i < postList.size(); i++) {
String Name = postList.get(i).getGamesName().toString();
mGamesName.add(Name);
}
} catch (Exception e) {
}
}
Log.d(TAG, "Returned count " + postList.size());
NewAdapter adapter = new NewAdapter(getApplicationContext(), postList);
recyclerView.setAdapter(adapter);
}
}
#Override
public void onFailure(Call<List<ApiObject>> call, Throwable t) {
//showErrorMessage();
Log.d(TAG, "error loading from API");
}
});
}
pass an interface
public interface ApiCallback{
void onSuccess(List<ApiObject> result);
}
and in on Create view of activity i called this
doRequest(new ApiCallback(){
#Override
public void onSuccess(List<ApiObject> result){
//here i can set variable values
}
});
the only thing came to mind is retrieving data can take time while your code lines are being read and finding null values as data has not been received yet.
That's entirely correct. Your call is finishing after you check the values. I'm going to go on a limb here and say that it's just a coincidence that it works on one app and not in the other (if they are actually doing it the same way)
When you call callback.onSuccess(postList); doesn't seem to be right either, because you haven't checked yet for success. This means that response.body() might be null and response.errorBody() will contain the body of the error.
If you'd move callback.onSuccess inside the if this would be fixed:
if(response.isSuccessful()) {
callback.onSuccess(response.body());
try {
for (int i = 0; i < postList.size(); i++) {
String Name = postList.get(i).getGamesName().toString();
mGamesName.add(Name);
}
} catch (Exception e) {
}
Last but not least, inside the onSuccess method is when you can use your global variables. Maybe it's better to stop using global variables and just use the callback parameters.
I'm trying to implementing this function with a customer classloader: I have some class files in a alternatives.jar file, they provide different implementation than normal implementation. i.e., each class in this jar, has another version which in other jar file -- also get loaded in the classpath.
I know it's better to use instrument API to achieve same purpose. But now my concern is I need to understand why I'm failing.
So this is my method:
1. define a AlternativeClassLoader.java, in this file, I override findClass method. So if the class name can be found from alternatives.jar, then use the version from alternatives.jar.
2. in constructor, I have called super(null) so all these class loading work will be performed by my classloader, rather that system's.
3. This (seems to be true) also requires me to load other classes (if they're not system one). So I have to parse classpath, find all classes which indicated by the classpath.
My problem is, I can load my alternative class, everything seems to be fine...However, I'm using slf4j which yells the following error:
Failed to auto configure default logger context
Reported exception:
ch.qos.logback.core.joran.spi.JoranException: Parser configuration error occurred
Failed to instantiate [ch.qos.logback.classic.LoggerContext]
Reported exception:
java.lang.ExceptionInInitializerError
at java.util.ResourceBundle.getLoader(ResourceBundle.java:431)
at java.util.ResourceBundle.getBundle(ResourceBundle.java:841)
I doubt this is caused by my bad classloader implementation. Would somebody help me out? Many thanks!
This is my classloader:
public class AlternativeClassLoader extends ClassLoader {
private static final String ALTERNATIVE_JAR_PROPERTY = "alternativejar";
private static final Logger logger = LoggerFactory
.getLogger(AlternativeClassLoader.class);
private Map<String, Class<?>> clzCache = new HashMap<String, Class<?>>();
private Map<String, String> others = new HashMap<String, String>();
private Set<String> alternativesRegistry;
private JarFile altjar;
public AlternativeClassLoader(ClassLoader parent) {
/*
* pass null so I can incept all class loading except system's. By doing
* this you'll need to override findClass
*/
super(null);
registerAlternatives();
registerOthers();
}
/**
* This method will parse classpath and get all non-system class name, and
* build classname - jar_file_path/file_system_path mappings
*/
private void registerOthers() {
String[] paths = System.getProperty("java.class.path").split(":");
URL[] urls = new URL[paths.length];
for (String path : paths) {
if (path.endsWith("*.jar")) {
registerClass(path, others);
} else {
File f = new File(path);
if (!f.isDirectory())
continue;
File[] classFiles = f.listFiles(new FileFilter() {
#Override
public boolean accept(File arg0) {
if (arg0.getName().endsWith(".class")) {
return true;
} else {
return false;
}
}
});
for (File file : classFiles) {
String fileName = file.getName();
String className = fileName.substring(0,
fileName.lastIndexOf("."));
others.put(className, file.getPath());
}
}
}
showRegistry(
"Me will also be responsible for loading the following classes:",
others);
}
private void registerClass(String path, Map<String, String> registry) {
try {
JarInputStream jis = new JarInputStream(new FileInputStream(path));
for (JarEntry entry = jis.getNextJarEntry(); entry != null; entry = jis
.getNextJarEntry()) {
if (entry.getName().endsWith(".class") && !entry.isDirectory()) {
StringBuilder className = new StringBuilder();
for (String part : entry.getName().split("/")) {
if (className.length() != 0)
className.append(".");
className.append(part);
if (part.endsWith(".class"))
className.setLength(className.length()
- ".class".length());
}
registry.put(className.toString(), path);
}
}
} catch (Exception e) {
e.printStackTrace(System.out);
logger.error(
"Failed when read/parse jar {}. Your class file may not been replaced by alternative implementation",
path, e);
}
}
/**
* Try to find alternative class implementation from jar file specified by
* ALTERNATIVE_JAR_PROPERTY. If it's not specified, then use same jar file
* where this classloader is loaded.
*/
private void registerAlternatives() {
String jarFilePath = System.getProperty(ALTERNATIVE_JAR_PROPERTY);
if (jarFilePath == null || jarFilePath.isEmpty()) {
URL url = getClass().getProtectionDomain().getCodeSource()
.getLocation();
System.out.println(url + ":" + url.toString());
jarFilePath = url.getPath();
}
try {
altjar = new JarFile(jarFilePath);
} catch (IOException e) {
logger.error("cannot read jar {}", jarFilePath);
return;
}
Map<String, String> registry = new HashMap<String, String>();
registerClass(jarFilePath, registry);
alternativesRegistry = registry.keySet();
showRegistry("===Found the following alternative class:===", registry);
}
private void showRegistry(String string, Map<String, String> registry) {
System.out.println(string);
for (String clzName : registry.keySet()) {
System.out.printf("Class:%30s ->%s\n", clzName,
registry.get(clzName));
}
}
private Class<?> myLoadClass(String name) throws IOException,
ClassFormatError {
logger.debug("myload class {}", name);
System.out.printf("myload class %s\n", name);
if (alternativesRegistry.contains(name) && altjar != null) {
JarEntry entry = altjar.getJarEntry(name + ".class");
InputStream is = altjar.getInputStream(entry);
return readClassData(name, is);
}
String path = others.get(name);
if (path == null || path.isEmpty()) {
return null;
}
if (path.endsWith(".jar")) {
JarFile jar = new JarFile(path);
JarEntry entry = jar.getJarEntry(name + ".class");
InputStream is = jar.getInputStream(entry);
return readClassData(name, is);
} else {// it's a folder, need to read clz from .class file
System.out.printf("file path for %s is %s\n", name, path);
InputStream is = new FileInputStream(new File(path));
return readClassData(name, is);
}
}
private Class<?> readClassData(String name, InputStream is)
throws IOException, ClassFormatError {
byte[] buffer = new byte[4096];
ByteArrayOutputStream out = new ByteArrayOutputStream(buffer.length);
int len = is.read(buffer);
while (len > 0) {
out.write(buffer, 0, len);
len = is.read(buffer);
}
Class<?> clz = defineClass(name, out.toByteArray(), 0, out.size());
if (clz != null) {
System.out.printf("loaded %s by me\n", name);
clzCache.put(name, clz);
}
return clz;
}
protected Class<?> findCachedClass(String name)
throws ClassNotFoundException {
Class<?> clz = clzCache.get(name);
if (clz == null) {
clz = findLoadedClass(name);
}
return clz;
}
#Override
protected Class<?> findClass(String name) throws ClassNotFoundException {
System.out.println("findClass: " + name);
Class<?> cls = findCachedClass(name);
if (cls == null) {
try {
cls = myLoadClass(name);
} catch (ClassFormatError | IOException e) {
logger.error("failed to load class {}", name, e);
System.out.printf("failed to load class %s\n", name);
e.printStackTrace();
}
}
return cls;
}
}
I have tried to override findResource(), but it's never called.
This is how I put my classloader into use:
java -Djava.system.class.loader=AlternativeClassLoader -classpath=.:./alternatives.jar:./slf4j-xxx.jar Test
OK, I solved the problem. The tricky is:
Never use any package other than java.*. Otherwise, it will cause recursively loading ...IllegalState error.
In your classloader constructor, load all the alternative class and cache them.
In your constructor, call super(parent) other than super(null), then you don't need to do all the class loading stuff, the parent classloader can do it for you.
in override findClass(), if the class can be found from cache (means they have alternative implementation), then return it, otherwise let super.findClass do the rest for you.
so the following is the source code:
public class AlternativeClassLoader extends ClassLoader {
private static final String ALTERNATIVE_JAR_PROPERTY = "alternativejar";
private Map<String, Class<?>> clzCache = new HashMap<String, Class<?>>();
public AlternativeClassLoader(ClassLoader parent) {
super(parent);
loadAlternativeClasses();
}
private void loadAlternativeClasses() {
String jarFilePath = System.getProperty(ALTERNATIVE_JAR_PROPERTY);
if (jarFilePath == null || jarFilePath.isEmpty()){
URL url = getClass().getProtectionDomain().getCodeSource().getLocation();
System.out.println(url + ":" + url.toString());
jarFilePath = url.getPath();
}
JarInputStream jis;
try {
jis = new JarInputStream(new FileInputStream(jarFilePath));
JarEntry entry;
while ((entry = jis.getNextJarEntry()) != null){
String className = entry.getName();
className = className.substring(0, className.length() - ".class".length());
System.out.printf("loading class from %s: %s\n", jarFilePath, className);
readClassData(className, jis);
}
} catch (IOException e) {
e.printStackTrace();
}
} private Class<?> readClassData(String name, InputStream is) throws IOException,
ClassFormatError {
byte[] buffer = new byte[4096];
ByteArrayOutputStream out = new ByteArrayOutputStream(buffer.length);
int len = is.read(buffer);
while (len > 0) {
out.write(buffer, 0, len);
len = is.read(buffer);
}
Class<?> clz = defineClass(name, out.toByteArray(), 0, out.size());
if (clz != null) {
System.out.printf("loaded %s by myself\n", name);
clzCache.put(name, clz);
}
return clz;
}
protected Class<?> findClass(String name) throws ClassNotFoundException {
System.out.println("findClass: " + name);
Class<?> cls = clzCache.get(name);
if (cls == null)
cls = super.findClass(name);
return cls;
}
}
I am writing up some tests for a C++ program and I would like to check that my program throws certain types of exceptions when given certain inputs. I have seen that this is doable using external libraries such as googletest, but I would like to know how this was implemented.
I would like to separate the test data from the test code as much as possible. In particular, I would like something like this:
void RunTests(InputList inputs) {
for (int i = 0; i < inputs.length; i++) {
if (FunctionIAmTesting(inputs[i].value) has the expected exception behavior) {
// Pass
} else {
// Fail
}
}
}
InputList inputs = InputList({
Input(5), // no exception when 5 is an input
Input<MyExceptionClass>(0), // MyExceptionClass thrown when 0 is an input
Input<MyOtherExceptionClass>(-1) // MyOtherExceptionClass thrown when -1 is an input
});
RunTests(inputs);
If you know what the type of exception you are looking for then you can target an exception of that type in the catch () statement.
try {
// Test code.
// Unexpected success
std::cerr << "Expected a RelevantException to be thrown." << std::endl;
}
catch (RelevantException& e)
{
// Expected exception, continue.
}
catch (...) // Catch all
{
// Unexpected exception
std::cerr << "Unexpected exception encountered, expected "
"RelevantException." << std::endl;
}
A several years back I wrote some simple library for "mocking" objects. And my goal was to check everything related to function calls. In the tests I wrote something like that:
MyMockedObject my;
mock::expect(my, "foo").in(10).out(20).returns(30);
mock::expect(my, "bar").throws(logic_error("bar failed"));
int v;
// test that my::baz() invokes my.foo(10, v)
// then my.bar which fails with the exception
my.baz();
Your task seems to be a little bit easier. All that you need is a way how to describe your expectations and some hack in the test runner to verify them at the end of a test (accordingly to the input). Your expectations are exceptions, just construct them somehow and associate with the input. In your example you did a half part of your work.
typedef std::map<Input, Exception> Expectations;
typedef std::pair<Input, Exception> Expectation;
// somewhere before the tests
expectations.insert(make_pair(Input(5)), NoThrowAnything);
expectations.insert(make_pair(Input(0)), MyException("some message"));
expectations.insert(make_pair(Input(-1)), MyOtherException("another message"));
void run_test(const Expectation& expect)
{
try {
// run the real test here based on Input (expect.first)
check_expectation(expect);
} catch (const Exception& ex) {
check_expectation(expect, ex);
}
}
void run_all_tests(const Expectations& expects)
{
for (e : expects) {
try {
run_test(e);
} catch (const ExpectationException ex) {
// failed expectation
}
}
}
void check_expectation(const Expectation& expect)
{
if (expect.second != NoThrowAnything) {
throw ExpectationFailure(expect);
}
}
void check_expectation(const Expectation& expect, const Exception& ex)
{
if (expect.second != ex) {
throw ExpectationMismatch(expect, ex);
}
}
I am writing some eclipse emf code and would like to print the content of an EObject (not store it to disk).
Here is what I try:
public static void print(EObject obj) {
Resource eResource = obj.eResource();
try {
eResource.save(System.out, null);
} catch (IOException e) {
e.printStackTrace();
}
}
but that gives a NullPointerException. I have tried this instead:
public static void print(EObject obj) {
ResourceSet resourceSet = new ResourceSetImpl();
resourceSet.getResourceFactoryRegistry().getProtocolToFactoryMap()
.put("*", new XMIResourceFactoryImpl());
Resource resource = resourceSet.createResource(URI.createURI("dummyfile.xml"));
resource.getContents().add(obj);
try {
resource.save(System.out, null);
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
This works, but is it not possible to print to screen without specifying a dummy URI??
Updated to include EcoreUtil.copy()
Check this code.
Resource res = new XMLResourceImpl ();
res.getContents().add(EcoreUtil.copy(obj));
try {
resource.save(System.out, null);
} catch (IOException ioe) {
ioe.printStackTrace();
}
If that fails then yes you need a dummy URI
Resource res = new XMLResourceImpl (URI.createURI("dummyfile.xml"));
res.getContents().add(EcoreUtil.copy(obj));
try {
resource.save(System.out, null);
} catch (IOException ioe) {
ioe.printStackTrace();
}
Hm when I pass a copy:
Resource res = new XMLResourceImpl ();
res.getContents().add(ECoreUtil.copy(obj));
try {
resource.save(System.out, null);
} catch (IOException ioe) {
ioe.printStackTrace();
}
some of the xmi attributes are not printed. But if I call the above method multiple times and DON't pass a copy I get a NullPointerException. I guess I am not understanding some basic EMF/Containment functionality here?
So my updated question is:
Is it possible to print a FULL EObject model without modifying the content if the model is used in the following code?