Creating a generic list using class object in java

Question

I have a function which i want to make generic. I want below code

public String list(){
    List<EMovieCategory> dataList = DBCompanyContent.getInstance().getDataByDocType(EMovieCategory.class);
    return "";
}

Be something like

public String list(Class cls){
        List<WHAT TO WRITE HERE > dataList = DBCompanyContent.getInstance().getDataByDocType(cls);
        return "";
    }

I couldn`t figure out what to write inside List<***>

You should find some tutorial about Generic type in Java. Because if you get an answer, you might not understand it at all. — AxelH
– AxelH, Commented Sep 29, 2017 at 8:06

Andy Turner · Accepted Answer · 2017-09-29 08:08:53Z

1

Use a type variable:

public <T> String list(Class<T> cls){
    List<T> dataList = DBCompanyContent.getInstance().getDataByDocType(cls);
    return "";
}

You might need to bound the type variable, if the getDataByDocType requires instances of Class within a certain bound:

public <T extends SomeClass> String list(Class<T> cls) {

OTOH, if you're not actually using the fact it's a list of Ts:

public String list(Class<?> cls){
    List<?> dataList = DBCompanyContent.getInstance().getDataByDocType(cls);
    return "";
}

or you don't even need a variable at all, if you're not going to use it:

public String list(Class<?> cls){
    DBCompanyContent.getInstance().getDataByDocType(cls);
    return "";
}

answered Sep 29, 2017 at 8:08

Andy Turner

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Comments

LW001 · Accepted Answer · 2017-09-29 08:07:03Z

0

The part between the <> is what data types the List will be storing. You'll be inputting what data type getDataByDocType(cls) returns.

answered Sep 29, 2017 at 8:07

LW001

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