CODEWITHSUNDEEP
javagenerics
Rajat Gupta
Rajat Gupta

Reputation: 26597

How to make this (generics) type specification work?

The following code works fine with generic type parameter Column but how do I make this work with type parameter Column<N> where N is type used for field columns.

    class Cols_Iterables2<Column> extends Iterable2<Column>{ 
        ColumnList<N> columns;

        public Cols_Iterables2(ColumnList<N> columnList) {
            this.columns = columnList;
        }

        @Override
        public Column get(int index) {
            return columns.getColumnByIndex(index);
        }
    }

Upvotes: 0

Views: 54

Answers (1)

Oleg Sklyar
Oleg Sklyar

Reputation: 10082

Assuming that your ColumnList<N> has the getColumnByIndex method defined roughly as follows

class ColumnList<N> {
   public Column<N> getColumnByIndex(int index) {

just parametrise your Cols_Iterables2 class with N:

class Cols_Iterables2<N> extends Iterable2<Column<N>> { 
    ColumnList<N> columns;

    public Cols_Iterables2(ColumnList<N> columnList) {
        this.columns = columnList;
    }

    @Override
    public Column<N> get(int index) {
        return columns.getColumnByIndex(index);
    }
}

Upvotes: 2

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