I have three java files(Login.java,Sales.java), and i want to pass a variable "Username" to other 3 java files so that the Sales.java can show the "Username"
This is what i done, build a loginstaff.java:
public class LoginStaff {
private String Username;
public void LoginStaff() {
}
public void LoginStaff(String Username) {
this.Username = Username;
}
public String getUsername() {
return this.Username;
}
public void setUserame(String Username) {
this.Username = Username;
}
}
In Login.java
...
String login = tfusername.getText();
LoginStaff loginstaff = new LoginStaff();
loginstaff.setUserame(login);
...
In Sales.java
...
LoginStaff loginstaff = new LoginStaff();
System.out.println(loginstaff.getUsername());
...
The problem is i cannot get the Username in Sales, it returned "null".
I know this is something related to new a object in different class, but i dont know how to fix this.
It's not a matter of where you're calling it - it's a matter of it being two different objects. This would demonstrate the same problem in a single method:
public void showProblem() {
LoginStaff staff1 = new LoginStaff();
// Assume typo in method name is fixed
staff1.setUsername("foo");
LoginStaff staff2 = new LoginStaff();
System.out.println(staff2.getUsername()); // Prints null
}
Two different objects will have two distinct sets of fields - that's deliberate and a good thing. You can't create a new object and expect it to have all the field values that you set on another object.
It sounds like fundamentally the problem is that you need your Sales code to know about the LoginStaff object created in your Login code. Without knowing more about your design, we can't really tell you the best way of achieving that.
If in one class you do this:
LoginStaff loginstaff = new LoginStaff();
loginstaff.setUserame(login);
And in the other class you do this:
LoginStaff loginstaff = new LoginStaff();
loginstaff.getUsername();
You are creating two different objects. Thus, for the second object, the UserName was never set. If you want to access the same object, you will need to reference it. A work around would be to pass a LoginStaff object around when the objects are initialized. This will allow you to access the same settings.
In Sales.java
...
LoginStaff loginstaff = new LoginStaff();
loginstaff.getUsername();
...
Here 1st line creates a new object with default initialization of variables, which is null in case of String type. Before using getUsername(), you have to call setUsername()
Or otherwise create a cunstrocter in Sales.java which accepts the LoginStaff object and after setting the username at Login.java, pass that object to Sales.java and in Sales.java instead of creating a new LoginStaff object, store the object passed by Login.java and then use getUsername()
When you create your sales object, I suggest you provide it with a MainClass(this) parameter. Obviously update your sales constructor to reflect this. This allows you to store an identical MainClass in your sales class, which you can use to query for name or whatever else you may need.
Basically Sales s1 = new Sales(this);
I have had a similar process where I had a UI bar class, but needed to start a method in the main class to act when the user clicked on a button in the UI. The way I did it was had a classwide field at the top of my main class.
so basically:
public class MainClass() {
private InterfaceTab interfaceTab;
//Instantiate the field in the constructor or main method of MainClass, so that way both classes can access each other:
interfaceTab = new InterfaceTab(this);
Related
I am creating my web page with vaadin where I need to create same kind of blocks for different type for example need to show blocks having car details, so only car name would be different but the block design would be same with same label but different labels. I want to write generic code so that i can expand it for any car name, without adding it manually.
Attaching the code snippet which i am using where i am repeating my code for different type. Want to implement it dynamically.
private Grid<PresentableGenerateInputHeaders> winTSHeaderColumnsGrid;
private Grid<PresentableGenerateInputHeaders> fRHeaderColumnsGrid;
private ListDataProvider<PresentableGenerateInputHeaders> listDataProvider;
private List<PresentableGenerateInputHeaders> presentableGenerateInputHeaders = new ArrayList<>();
private void initWinTsGrid() {
listDataProvider = new ListDataProvider<>(presentableGenerateInputHeaders);
winTSHeaderColumnsGrid = new Grid<PresentableGenerateInputHeaders>(PresentableGenerateInputHeaders.class);
winTSHeaderColumnsGrid.setDataProvider(listDataProvider);
winTSHeaderColumnsGrid.setCaption(i18n.get("view.ruleDetails.general.csvHeaderColumns"));
winTSHeaderColumnsGrid.setStyleName("a-units");
winTSHeaderColumnsGrid.setWidth("450px");
winTSHeaderColumnsGrid.setItems(addGridValues(DataSource.WIN_TS, winTSHeaderColumnsGrid));
winTSHeaderColumnsGrid.getEditor().setEnabled(true);
winTSHeaderColumnsGrid.setColumnOrder("header", "count");
winTSHeaderColumnsGrid.sort("header");
winTSHeaderColumnsGrid.getEditor().addSaveListener((EditorSaveEvent<PresentableGenerateInputHeaders> event) -> {
event.getGrid().select(event.getBean());
selectedGapFillingCountWINTS.add(event.getBean());
});
}
private void initFRGrid() {
listDataProvider = new ListDataProvider<>(presentableGenerateInputHeaders);
fRHeaderColumnsGrid = new Grid<PresentableGenerateInputHeaders>(PresentableGenerateInputHeaders.class);
fRHeaderColumnsGrid.setDataProvider(listDataProvider);
fRHeaderColumnsGrid.setCaption(i18n.get("view.ruleDetails.general.csvHeaderColumns"));
fRHeaderColumnsGrid.setStyleName("a-units");
fRHeaderColumnsGrid.setWidth("450px");
fRHeaderColumnsGrid.setItems(addGridValues(DataSource.FR, fRHeaderColumnsGrid));
fRHeaderColumnsGrid.getEditor().setEnabled(true);
fRHeaderColumnsGrid.setColumnOrder("header", "count");
fRHeaderColumnsGrid.sort("header");
fRHeaderColumnsGrid.getEditor().addSaveListener((EditorSaveEvent<PresentableGenerateInputHeaders> event) -> {
event.getGrid().select(event.getBean());
selectedGapFillingCountFR.add(event.getBean());
});
}
You can change methods to be more generic by identifying all the parts you don't want to keep static, and moving those to be populated by method parameters instead. I.e. instead of
private void myMethod() {
grid.setCaption("myCaption");
}
you would write
private void myMethod(String caption) {
grid.setCaption(caption);
}
and then call it
myMethod("myCaption");
If you need to be outside of the whole class to be able to determine what the real values are, you can for example make the method public or pass on the necessary values in the class constructor.
public MyClass(String gridCaption) {
myMethod(gridCaption);
}
If there are a lot of values you need to set dynamically, you might consider using an object that contains all the necessary values instead.
public void myMethod(MyPojo pojo) {
grid.setCaption(pojo.getGridCaption());
}
In your example it looks like the generic values you want to pass are DataSource dataSource and whatever type of collection selectedGapFillingCountWINTS and selectedGapFillingCountFR happen to be, and the method should probably return the grid rather than set it directly to a class variable.
So I am creating a chat app for android and I'm using Java and I need some help wrapping my head around some things. Whenever the user first registers, I am creating a new object of a class named User. When they enter the next layout, I need to access that objects data.
public class User {
public String username;
public User() {}
public User(String username) {
this.username = username;
}
public String getUsername(){
return username;
}
}
This is my User class. When they send a message, I need to be able to grab their username from this User object from an entirely different method without passing the object through a parameter. I can't seem to wrap my head around how to access their information and none of my methods seem to work. Any help is appreciated
If you do
User myUser = new User();
the variable myUser contains a reference to the newly created object. You must keep this reference around in order to later access the object. How exactly you do this depends on the logic of your program. Sometimes you would keep it in a field of another object or pass it around as parameter. For example
un = myUser.getUsername();
or
void myMethod(User theUser) {
...
String un = theUser.getUsername();
}
...
// call the method passing the user reference
myMethod(myUser);
in the main class make the data object... static
public static Model obj;
obj= new Model();
then from other class access it with your class name
example
main.obj;
I solved this issue by just using SharedPreferences. I stored the username associated with the key of each user. This way, I can always search the username for each user.
I need to unit test a method, and I would like mock the behavior so that I can test the necessary part of the code in the method.
For this I would like access the object returned by a private method inside the method I am trying to test. I created a sample code to give a basic idea of what I am trying to achieve.
Main.class
Class Main {
public String getUserName(String userId) {
User user = null;
user = getUser(userId);
if(user.getName().equals("Stack")) {
throw new CustomException("StackOverflow");
}
return user.getName();
}
private User getUser(String userId) {
// find the user details in database
String name = ""; // Get from db
String address = ""; // Get from db
return new User(name, address);
}
}
Test Class
#Test (expected = CustomException.class)
public void getUserName_UserId_ThrowsException() {
Main main = new Main();
// I need to access the user object returned by getUser(userId)
// and spy it, so that when user.getName() is called it returns Stack
main.getUserName("124");
}
There are only two ways to access private:
using reflection
extend the scope
maybe waiting for Java 9 to use new scope mechanisms?
I would change the scope modifier from private to package scope. Using reflection is not stable for refactoring. It doesn't matter if you use helpers like PowerMock. They only reduce the boiler-plate code around reflection.
But the most important point is you should NOT test too deep in whitbox tests. This can make the test setup explode. Try to slice your code into smaller pieces.
The only information the method "getUserName" needs from the User-object is the name. It will validate the name and either throw an exception or return it. So it should not be necessary to introduce a User-object in the test.
So my suggestion is you should extract the code retreiving the name from the User-object into a separate method and make this method package scope. Now there is no need to mock a User-Object just the Main-Object. But the method has its minimal information available to work properly.
class Main {
public String getUserName(String userId) {
String username = getUserNameFromInternal(userId);
if (userName.equals("Stack")) {
throw new CustomException("StackOverflow");
}
return user.getName();
}
String getUserNameFromInternal(String userId) {
User user = getUser(userId);
return user.getName();
}
...
}
The test:
#Test (expected = CustomException.class)
public void getUserName_UserId_ThrowsException() {
Main main = Mockito.mock(new Main());
Mockito.when(main.getUserNameInternal("124")).thenReturn("Stack");
main.getUserName("124");
}
Your problem that call to new within your private method.
And the answer is not to turn to PowerMock; or to change the visibility of that method.
The reasonable answer is to "extract" that dependency on "something that gives me a User object" into its own class; and provide an instance of that class to your "Main" class. Because then you are able to simply mock that "factory" object; and have it do whatever you want it to do.
Meaning: your current code is simply hard-to-test. Instead of working around the problems that are caused by this, you invest time in learning how to write easy-to-test code; for example by watching these videos as a starting point.
Given your latest comment: when you are dealing with legacy code, then you are really looking towards using PowerMockito. The key part to understand: you don't "mock" that private method; you rather look into mocking the call to new User() instead; as outlined here.
You can use a PowerMock's mockPrivate but I don't recommend it.
If you has such a problem it usually mean that your design is bad.
Why not making the method protected?
I have a method where I want to factor out some code into its own method
This is what I have:
public class TD0301AssignmentForm extends Form {
public TD0301AssignmentForm(TD0301AssignmentDAO dao, STKUser authenticatedUser) {
this.dao = dao;
this.authenticatedUser = authenticatedUser;
}
public Object insert(HttpServletRequest request) {
TD0301Assignment tdas = new TD0301Assignment();
TD0301Assignment tdas_orig = null;
Date dateNow = new Date();
try {
// Get the inuput from HTML form
tdas.setCalc_num(FormUtil.getFieldValue(request, FIELD_CALC_NUM));
processDate(request, tdas);
tdas.setCalc_dept(FormUtil.getFieldValue(request, FIELD_CALC_DEPT));
tdas.setYear_oi(Integer.toString(DateUtil.getIntYear(dateNow)));
processCalcSafetyRequirements(request, tdas);
...etc...
if (isSucces()) {
// Instantiate a base work flow instance!
WorkflowInstance wfi = new WorkflowInstance();
WorkflowInstanceDAO wfiDAO = new WorkflowInstanceDAO();
wfi.setWorkflow_class_id(tdas.getCalc_level());
wfi.setStarted_by(authenticatedUser.getBadge());
wfi.setStatus("0");
wfi.setLast_date(dateNow);
// Insert the WorkFlowInstance into the database, db sets returned sequence number into the wfi object.
wfiDAO.insert(wfi, authenticatedUser);
// Insert the TD0301Assignment into the db
tdas.setWorkflow_instance_id(wfi.getWorkflow_instance_id());
}
I'd like to remove the WorkflowInstance code out into its own method (still in this Class) like this:
if (isSucces()) {
insertWorkFlowInstance(request, tdas);
tdas.setWorkflow_instance_id(wfi.getWorkflow_instance_id());
but wfi is now marked by Eclipse as not available. Should I do something like this to fix the error so that I can still get the wfi.getWorkflow_instance_id() in the isSuccess block above? I know it removes the error, but I am trying to apply best practices.
public class TD0301AssignmentForm extends Form {
private WorkflowInstance wfi = new WorkflowInstance();
private WorkflowInstanceDAO wfiDAO = new WorkflowInstanceDAO();
Instance variables ("properties" or "fields") are not necessarily the way to go if they're not used throughout the entire class.
Variables should have the smallest scope possible--this makes code easier to reason about.
With some noise elided, and also guessing, it seems like the WorkflowInstance and WorkflowInstanceDao could be localized (names changed to match Java conventions):
public class TD0301AssignmentForm extends Form {
public Object insert(HttpServletRequest request) {
TD0301Assignment tdas = new TD0301Assignment();
try {
tdas.setCalcNum(FormUtil.getFieldValue(request, FIELD_CALC_NUM));
processDate(request, tdas);
tdas.setCalcDept(FormUtil.getFieldValue(request, FIELD_CALC_DEPT));
tdas.setYearOi(Integer.toString(DateUtil.getIntYear(dateNow)));
processCalcSafetyRequirements(request, tdas);
if (isSuccess()) {
WorkflowInstance wf = buildWorkflow(tdas);
tdas.setWorkflowInstanceId(wf.getId());
}
}
}
private buildWorkflow(TD0301Assignment tdas) {
WorkflowInstance wfi = new WorkflowInstance();
wfi.setWorkflowClassId(tdas.getCalcLevel());
wfi.setStartedBy(authenticatedUser.getBadge());
wfi.setStatus("0");
wfi.setLastDate(new Date());
WorkflowInstanceDao wfiDao = new WorkflowInstanceDao();
wfiDao.insert(wfi, authenticatedUser);
}
}
Whether or not this is appropriate depends on how/if the WorkflowInstance is used in the rest of the method snippet you show. The DAO is almost certainly able to be localized.
As methods become smaller and easier to think about, they become more testable.
For example, buildWorkflow is almost easy to test, except that the DAO is instantiated "manually". This means that testing the method will either (a) depend on having a working DAO layer, or (b) it must be mocked by a framework that can mock static utility methods (several can).
Without seeing all your code it's not easy to see exactlywhat you are trying to achieve. The reason eclipse is complaining is because it no longer has a wfi instance to play with because you've moved its local instance into your method, but creating another wfi instance is not likely to be your answer.
To get this working change the wfi to be class local and either use it's id directly or return wfi.getWorkflow_instance_id() from insertWorkFlowInstance() and then pass that value into tdas.setWorkflow_instance_id()
I'm learning Java at the moment so I hope this question isn't too obvious. I come from another language which does not have garbage collection.
In this other language I sometimes created objects in constructor and then deleted them in the destructor so I could use them for the entire life of the object.
As a simplified example, I have a user and a booking class. The booking class references a user but if I create the user in the constructor of the booking class, it dereferences the user once it leaves the constructor and becomes out of scope. Any future reference call to the booking.bookedBy user then returns null.
class user {
public String username;
public String displayName;
user(Connection conn, String usernameIn){
username = usernameIn;
... do DB stuff to populate attributes
}
}
class booking {
int bookingID;
user bookedBy;
...
booking(Connection conn, int bookedIDIn){
bookingID = bookedIDIn;
...do DB stuff to populate attributes and grab bookedByUserID
...field value and build the BookedByUsername
user bookedBy = new user (bookedByUsername)
}
}
Is there a way around this? Or do I need to rethink my design?
You are creating a new bookedBy user variable in your constructor, rather than using your class' member variable.
You probably want to change:
user bookedBy = new user(bookedByUsername);
with:
bookedBy = new user(bookedByUsername);
You're declaring a local variable in your constructor and it's being used to assign the user you create in the constructor.
I think you want this:
class booking {
int bookingID;
user bookedBy;
...
booking(Connection conn, int bookedIDIn){
bookingID = bookedIDIn;
//there's no declaration of type needed here because
//you did that earlier when you declared your member variable up top.
bookedBy = new user (bookedByUsername)
}
}
In your booking class, you actually have declared two variables called user bookedBy. One has scope for the entire booking class and one has scope for the constructor. To fix this problem, you need to remove the variable declaration in your constructor as show below:
class booking {
int bookingID;
user bookedBy;
...
booking(Connection conn, int bookedIDIn){
bookingID = bookedIDIn;
...do DB stuff to populate attributes and grab bookedByUserID
...field value and build the BookedByUsername
bookedBy = new user (bookedByUsername)
}
}
user bookedBy;
and
user bookedBy = new user (bookedByUsername)
are two different variables.
Remove the second type declaration and your user instance will be allocated to the field level. ie:
class booking {
int bookingID;
user bookedBy;
...
booking(Connection conn, int bookedIDIn){
bookingID = bookedIDIn;
...do DB stuff to populate attributes and grab bookedByUserID
...field value and build the BookedByUsername
bookedBy = new user (bookedByUsername)
}
}