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How to check if string is empty

I have an activity 'B'. I have 2 more activities A and C. Both the activities lead to B. But i pass different Data from A and C. So while fetching
String dataFromA = getIntent.getStringExtra("SomethingA");
String dataFromC = getIntent.getStringExtra("SomethingC");
How to not get an error. I wont know from where the user is getting to activity B So how do i add an If statement or seomthing to not get an error while fetching as Either line A or C will get a NullPOinterException

You can use hasExtra method to check if that String exists.
if (getIntent().hasExtra("SomethingA")) {
String dataFromA = getIntent.getStringExtra("SomethingA");
} else if (getIntent().hasExtra("SomethingC")) {
String dataFromC = getIntent.getStringExtra("SomethingC");
}

You can try this code.
Bundle arguments = getArguments();
if (arguments != null){
if (arguments.containsKey("SomethingA")) {
String somethingA = arguments.getString("SomethingA");
if (TextUtils.isEmpty(somethingA)){
// Your codes comes here
}
}
}
Bundle (arguments) can be null if there is no data passed.

To check if string is empty or not use below code :
if(TextUtils.isEmpty(yourString))
{
// String empty
}
else
{
// string not empty
}
In your case you check it as :
if (getIntent()!=null && getIntent().getStringExtra!=null )
{
if (getIntent().hasExtra("SomethingA") && getIntent().hasExtra("SomethingB"))
String dataFromA = getIntent.getStringExtra("SomethingA");
String dataFromB = getIntent.getStringExtra("SomethingB");
}

GAE Query with Collection Parameter

I have verified that the entity I am looking for is in the datastore. I have verified that the list I pass as a method parameter contains this entity. I am trying to find all objects that have their 'userGmail' contained in the list of strings I pass.
Here is my code
#SuppressWarnings("unchecked")
#ApiMethod(name = "findFriendsByEmailList")
public CollectionResponse<ZeppaUser> findFriendsByEmailList(
#Named("emailsList") List<String> emailsList, User user)
throws OAuthRequestException {
if (user == null) {
throw new OAuthRequestException(
"Null User Authorization Exception, findFriendsByEmailList");
}
PersistenceManager mgr = null;
List<ZeppaUser> execute = null;
Query query = null;
try {
mgr = getPersistenceManager();
query = mgr.newQuery(ZeppaUser.class);
query.declareParameters("java.util.List emailListParam");
query.setFilter("emailListParam.contains( userGmail )");
execute = (List<ZeppaUser>) query.execute(emailsList);
query.closeAll();
} finally {
mgr.close();
}
return CollectionResponse.<ZeppaUser> builder().setItems(execute)
.build();
}
This is the stack trace I receive from it:
Something worth noting: I do not receive this error on lists I pass in that to not contain an element found in the datastore. Just when it does exist which leads me to believe that the Query has located the element but has not been closed or executed into a return parameter correctly. If it is preferable to return List that is more than ok. I have tried multiple variations of this with no success thus far. It is getting quite frustrating.

Ok so I found a way around it.
Lists cannot be passed into ApiEndpoints. That or I didn't figure out the correct way to do it and would LOVE an update on the proper way to do this.
Instead, in my client, I construct a String of emails seperated by a comma and send a string into the parameter as an 'encoded' string list then 'decode' it upon execution. Works well but seems hacky.
here are the methods I used. This is convenient though because it works with iOS as well.
public static String encodeListString(ArrayList<String> stringList){
StringBuilder stringbuilder = new StringBuilder();
stringbuilder.append(stringList.get(0));
if(stringList.size() > 1){
for( int i = 0; i < stringList.size(); i++){
stringbuilder.append(",");
stringbuilder.append(stringList.get(i));
}
}
return stringbuilder.toString();
}
public static List<String> decodeListString(String encodedString){
char[] characters = encodedString.toCharArray();
StringBuilder stringbuilder = new StringBuilder();
int position = 0;
ArrayList<String> stringList = new ArrayList<String>();
while(true){
try {
char character = characters[position];
if(character == ','){
String resultString = stringbuilder.toString();
stringList.add(resultString);
stringbuilder = new StringBuilder(); // clear it
} else {
stringbuilder.append(character);
}
position++;
} catch (ArrayIndexOutOfBoundsException aiex){
// List ended
String resultString = stringbuilder.toString();
if(!resultString.isEmpty())
stringList.add(resultString);
break;
}
}
return stringList;
}

How to convert from JSObject to Map (viceversa) or list JSObject members

In Javascript i have the following code:
var r=applet.foo({var0:99,var1:'foo',var2:applet});
In my Java applet i have the following:
public JSObject foo(JSObject args){
System.out.println("The function is correctly invoked");
//In fact, the following works perfectly:
System.out.println("var1 is:"+(String)args.getMember("var1"));
JSObject w=JSObject.getWindow(this);
JSObject j=(JSObject)w.eval("new Object();");
Map m=new Hashmap();
//TODO here all the keys and values of args should be added to m
m.put("hello","world");
//TODO here all the keys and values of m should be added to j
return j;
}
How can this be done? (TODOs)
Reading http://docstore.mik.ua/orelly/web/jscript/ch19_06.html, i noticed theres a getSlot method for JSObject but if i do
args.getSlot(0)
all i have is one Exception:
netscape.javascript.JSException: No such slot 0 on JavaScript object
...

Unfortunately, Errandir's solution works only when you know a name of global variable that can be used to access an object you want to get properties' names of. You need to know this name to be able to add keys method to the object, and invoke it using JSObject's call method later. Of course, you can pass a global name of your object to Java if you have it. This solution doesn't look so good especially when you can't refer to your object in global context.
As an alternative, I proposed to use this of JSObject's eval method in the comment supposing that it will do all the work. And it does. But a big disappointent was that it works as expected only in Mozilla Firefox and Opera. In Internet Explorer 9 and Google Chrome (tested under Windows 7 and Ubuntu 12.04 LTS) this of eval method always refers to applet's document window ignoring which JavaScript object JSObject instance actually represents. I don't know whether it's a bug or simply LiveConnect is supported in these browsers very poorly.
The good news is that call method of JSObject executes specified function on the proper context. Keeping that in mind I finally found a solution how a list of names of JavaScript object's properties can be retrieved. The idea is to define a temporary function in global context using eval method. This function has to receive a JavaScript object we want to get properties of and to return names of these properties as an array. After that we can invoke the temporary function through JSObject's call method passing a Java representation of concerned JavaScript object (jsObject in my method below or args as it sounds in the question). At last, temporary function can be removed.
public static ArrayList<String> getJsObjectPropertiesNames(Applet applet, JSObject jsObject) {
if (applet == null || jsObject == null)
return null;
// Retrieving global context - a JSObject representing a window applet belongs to
JSObject globalContext;
try {
globalContext = JSObject.getWindow(applet);
}
catch (JSException ex) {
return null;
}
// Checking whether passed object is not an array
try {
jsObject.getSlot(0);
return null;
}
catch (JSException e) {
}
String keysFunctionName = String.format("_getKeys%d", Calendar.getInstance().getTimeInMillis());
jsObject.eval("window['" + keysFunctionName + "'] = function(jsObject) { return Object.keys(jsObject) }");
JSObject propertiesNamesJsObject = (JSObject)globalContext.call(keysFunctionName, new Object[] { jsObject });
jsObject.eval("delete(window['" + keysFunctionName + "'])");
ArrayList<String> propertiesNames = new ArrayList<>();
try {
int slotIndex = 0;
while (true) {
Object propertyName = propertiesNamesJsObject.getSlot(slotIndex);
if (propertyName instanceof String)
propertiesNames.add((String)propertyName);
slotIndex++;
}
}
catch (JSException e) {
}
return propertiesNames;
}

As a solution, you could define method keys as proposed here (You can do it within your java-code using JSObject.eval(...)). Then you could get keys like:
JSObject keys = (JSObject)args.call("keys", Collections.EMPTY_LIST);
keys.getSlot(0);

Here below I print a String, please modify it to get whatever you need.
public final static String getKeys = "{var keys = [];for (var key in this) {keys.push(key);} keys;}";
private static String printProperties(final Object o,
final boolean printType,
final int level,
final String tab) {
final StringBuilder sb = new StringBuilder(100);
if (printType) {
sb.append("(");
sb.append(o.getClass().getSimpleName());
sb.append(") ");
}
if (o instanceof JSObject) {
sb.append("{\n");
final JSObject js = (JSObject) o;
final JSObject keys = (JSObject) js.eval(getKeys);
boolean needComma = false;
for (int i = 0;; i++) {
final String key = (String) keys.getSlot(i);
if ((key != null) && !(key.equals("undefined"))) {
final Object val = js.getMember(key);
if (!needComma) {
needComma = true;
} else {
sb.append(",\n");
}
sb.append(multitab(tab, level));
sb.append(key);
sb.append(":");
sb.append(printProperties(val, printType, level + 1, tab));
} else {
break;
}
}
sb.append("\n");
sb.append(multitab(tab, level - 1));
sb.append("}");
} else {
sb.append(o);
}
return sb.toString();
}
private final static String tab = " ";
private static String multitab(final String tab,
int i) {
final StringBuilder sb = new StringBuilder();
while (i-- > 0) {
sb.append(tab);
}
return sb.toString();
}

Use JDT to get full method name

I am new to eclipse plugin development and I am trying to convert a IMethod to a string representation of the full method name. I.E.
my.full.package.ClassName.methodName(int param, String string)
so far I have had to hand roll my own solution. Is there a better way?
private static String getMethodFullName(IMethod iMethod)
{
String packageString = "[Default Package]";
try {
IPackageDeclaration[] declarations = iMethod.getCompilationUnit().getPackageDeclarations();
if(declarations.length > 0)
{
packageString = declarations[0].getElementName();
}
} catch (JavaModelException e) {
}
String classString = iMethod.getCompilationUnit().getElementName();
classString = classString.replaceAll(".java", "");
String methodString = iMethod.getElementName() + "(";
for (String type : iMethod.getParameterTypes()) {
methodString += type + ",";
}
methodString += ")";
return packageString + "." + classString + "." + methodString;
}

You can get the Fully qualified name for the type using
method.getDeclaringType().getFullyQualifiedName();
This is probably easier than accessing the package from the compilation unit. The rest of you function looks correct.
One small point: you should use StringBuilder to build up the string instead of adding to a standard String. Strings are immutable so addition creates loads of unrecesary temparary objects.
private static String getMethodFullName(IMethod iMethod)
{
StringBuilder name = new StringBuilder();
name.append(iMethod.getDeclaringType().getFullyQualifiedName());
name.append(".");
name.append(iMethod.getElementName());
name.append("(");
String comma = "";
for (String type : iMethod.getParameterTypes()) {
name.append(comma);
comma = ", ";
name.append(type);
}
name.append(")");
return name.toString();
}

Thanks to iain and some more research I have come up with this solution. It seems like something like this should be built into the JDT....
import org.eclipse.jdt.core.Signature;
private static String getMethodFullName(IMethod iMethod)
{
StringBuilder name = new StringBuilder();
name.append(iMethod.getDeclaringType().getFullyQualifiedName());
name.append(".");
name.append(iMethod.getElementName());
name.append("(");
String comma = "";
String[] parameterTypes = iMethod.getParameterTypes();
try {
String[] parameterNames = iMethod.getParameterNames();
for (int i=0; i<iMethod.getParameterTypes().length; ++i) {
name.append(comma);
name.append(Signature.toString(parameterTypes[i]));
name.append(" ");
name.append(parameterNames[i]);
comma = ", ";
}
} catch (JavaModelException e) {
}
name.append(")");
return name.toString();
}

I am not sure it would take into account all cases (method within an internal class, an anonymous class, with generic parameters...)
When it comes to methods signatures, the classes to look into are:
org.eclipse.jdt.internal.corext.codemanipulation.AddUnimplementedMethodsOperation
org.eclipse.jdt.internal.corext.codemanipulation.StubUtility2
You need to get the jdt.core.dom.IMethodBinding, from which you can extract all what you need.
If you have a MethodInvocation, you can:
//MethodInvocation node
ITypeBinding type = node.getExpression().resolveTypeBinding();
IMethodBinding method=node.resolveMethodBinding();

Java toString() using reflection?

I was writing a toString() for a class in Java the other day by manually writing out each element of the class to a String and it occurred to me that using reflection it might be possible to create a generic toString() method that could work on ALL classes. I.E. it would figure out the field names and values and send them out to a String.
Getting the field names is fairly simple, here is what a co-worker came up with:
public static List initFieldArray(String className) throws ClassNotFoundException {
Class c = Class.forName(className);
Field field[] = c.getFields();
List<String> classFields = new ArrayList(field.length);
for (int i = 0; i < field.length; i++) {
String cf = field[i].toString();
classFields.add(cf.substring(cf.lastIndexOf(".") + 1));
}
return classFields;
}
Using a factory I could reduce the performance overhead by storing the fields once, the first time the toString() is called. However finding the values could be a lot more expensive.
Due to the performance of reflection this may be more hypothetical then practical. But I am interested in the idea of reflection and how I can use it to improve my everyday programming.

Apache commons-lang ReflectionToStringBuilder does this for you.
import org.apache.commons.lang3.builder.ReflectionToStringBuilder
// your code goes here
public String toString() {
return ReflectionToStringBuilder.toString(this);
}

Another option, if you are ok with JSON, is Google's GSON library.
public String toString() {
return new GsonBuilder().setPrettyPrinting().create().toJson(this);
}
It's going to do the reflection for you. This produces a nice, easy to read JSON file. Easy-to-read being relative, non tech folks might find the JSON intimidating.
You could make the GSONBuilder a member variable too, if you don't want to new it up every time.
If you have data that can't be printed (like a stream) or data you just don't want to print, you can just add #Expose tags to the attributes you want to print and then use the following line.
new GsonBuilder()
.setPrettyPrinting()
.excludeFieldsWithoutExposeAnnotation()
.create()
.toJson(this);

W/reflection, as I hadn't been aware of the apache library:
(be aware that if you do this you'll probably need to deal with subobjects and make sure they print properly - in particular, arrays won't show you anything useful)
#Override
public String toString()
{
StringBuilder b = new StringBuilder("[");
for (Field f : getClass().getFields())
{
if (!isStaticField(f))
{
try
{
b.append(f.getName() + "=" + f.get(this) + " ");
} catch (IllegalAccessException e)
{
// pass, don't print
}
}
}
b.append(']');
return b.toString();
}
private boolean isStaticField(Field f)
{
return Modifier.isStatic(f.getModifiers());
}

If you're using Eclipse, you may also have a look at JUtils toString generator, which does it statically (generating the method in your source code).

You can use already implemented libraries, as ReflectionToStringBuilder from Apache commons-lang. As was mentioned.
Or write smt similar by yourself with reflection API.
Here is some example:
class UniversalAnalyzer {
private ArrayList<Object> visited = new ArrayList<Object>();
/**
* Converts an object to a string representation that lists all fields.
* #param obj an object
* #return a string with the object's class name and all field names and
* values
*/
public String toString(Object obj) {
if (obj == null) return "null";
if (visited.contains(obj)) return "...";
visited.add(obj);
Class cl = obj.getClass();
if (cl == String.class) return (String) obj;
if (cl.isArray()) {
String r = cl.getComponentType() + "[]{";
for (int i = 0; i < Array.getLength(obj); i++) {
if (i > 0) r += ",";
Object val = Array.get(obj, i);
if (cl.getComponentType().isPrimitive()) r += val;
else r += toString(val);
}
return r + "}";
}
String r = cl.getName();
// inspect the fields of this class and all superclasses
do {
r += "[";
Field[] fields = cl.getDeclaredFields();
AccessibleObject.setAccessible(fields, true);
// get the names and values of all fields
for (Field f : fields) {
if (!Modifier.isStatic(f.getModifiers())) {
if (!r.endsWith("[")) r += ",";
r += f.getName() + "=";
try {
Class t = f.getType();
Object val = f.get(obj);
if (t.isPrimitive()) r += val;
else r += toString(val);
} catch (Exception e) {
e.printStackTrace();
}
}
}
r += "]";
cl = cl.getSuperclass();
} while (cl != null);
return r;
}
}

Not reflection, but I had a look at generating the toString method (along with equals/hashCode) as a post-compilation step using bytecode manipulation. Results were mixed.

Here is the Netbeans equivalent to Olivier's answer; smart-codegen plugin for Netbeans.