Java Generics Class as method parameter

Question

I have a TabListener in Android defined in this way:

public static class TabListener<T extends Fragment> 
    implements ActionBar.TabListener { ... }

An I have this source code:

Tab myTab = myActionBar.
                newTab().
                setText("Home").
                setTabListener(new TabListener<MyFragment>(
                    this, 
                    "Home", 
                    MyFragment.class
                ));
...

Now I want to put this into a method:

addTab("Home", ???);

private void addTab(String text, ???) {
    Tab myTab = myActionBar.
                newTab().
                setText(text).
                setTabListener(new TabListener<???>(
                    this, 
                    text, 
                    ???.class
                ));
    ...
}

What I have to fill in instead of ????

Bob Wang · Accepted Answer · 2013-02-28 17:54:50Z

5

Your tab listener needs the type parameter to be a subclass of Fragment

public static class TabListener<T extends Fragment>

Therefore, you need to make sure it is the case in your code

addTab("Home", ???);

private <T extends Fragment> void addTab(String text, Class<T> clazz) {
    Tab myTab = myActionBar.
                newTab().
                setText(text).
                setTabListener(new TabListener<T>(
                    this, 
                    text, 
                    clazz
                ));
    ...
}

answered Feb 28, 2013 at 17:54

Bob Wang

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Comments

irreputable · Accepted Answer · 2013-02-28 17:49:47Z

3

addTab("Home", MyFragment.class);

private void addTab(String text, Class<? extends Fragment> clazz) {
    Tab myTab = myActionBar.
            newTab().
            setText(text).
            setTabListener(new TabListener<>(
                this, 
                text, 
                clazz
            ));
    ...
}

answered Feb 28, 2013 at 17:49

irreputable

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2 Comments

Tim Over a year ago

Unfortunately, I use JRE6: '<>' operator is not allowed for source level below 1.7

irreputable Over a year ago

that can be solved by introducing a factory method. but it's fine to have a <T> to addTab()

Alan Krueger · Accepted Answer · 2013-02-28 17:25:41Z

2

Something like this is probably what you're looking for:

private <T> void addTab(String text, Class<T> clazz) {
    Tab myTab = myActionBar.
            newTab().
            setText(text).
            setTabListener(new TabListener<T>(
                this, 
                text, 
                clazz
            ));
    ...
}

answered Feb 28, 2013 at 17:25

Alan Krueger

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3 Comments

irreputable Over a year ago

wildcard is better. and the class should be a subclass of Fragment

Tim Over a year ago

I get this error here new TabListener<T>:

Bound mismatch: The type T is not a valid substitute for the bounded parameter <T extends Fragment> of the type MyActivity.TabListener<T>

Tim Over a year ago

This way, it works: private <T extends Fragment> void addTab(String text, Class<T> clazz)

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