Re: Java Collections List : Converting from List '<Column <String1, String2>>' to 'List <String1>'

But you can accomplish much the same sort of thing, albeit with not
quite as concise a call site (but at least the entire collection doesn't
have to be duplicated). For example:

public interface Select<T, S>
{
S select(T t);
}

public class Iterables
{
public static <T, S> Iterable<S> Select(Iterable<T> source, Select<T, S>
select)
{
return new SelectIterable<T, S>(source, select);
}

private static class SelectIterable<T, S> implements Iterable<S>
{
private final Iterable<T> source;
private final Select<T, S> select;

public SelectIterable(Iterable<T> source, Select<T, S> select)
{
this.source = source;
this.select = select;
}

@Override
public java.util.Iterator<S> iterator()
{
return new Iterator(source.iterator());
}

private class Iterator implements java.util.Iterator<S>
{
private final java.util.Iterator<T> source;

public Iterator(java.util.Iterator<T> source)
{
this.source = source;
}

@Override
public boolean hasNext()
{
return source.hasNext();
}

@Override
public S next()
{
return SelectIterable.this.select.select(source.next());
}

@Override
public void remove()
{
throw new UnsupportedOperationException();
}
}
}
}

public class Column
{
private final String string1;
private final String string2;

public Column(String string1, String string2)
{
this.string1 = string1;
this.string2 = string2;
}

public String getString1() { return string1; }
public String getString2() { return string2; }
}

import java.util.ArrayList;
import java.util.List;

public class Main
{

/**
* @param args
*/
public static void main(String[] args)
{
List<Column> columns = new ArrayList<Column>();

columns.add(new Column("1", "A"));
columns.add(new Column("2", "B"));
columns.add(new Column("3", "C"));

method2(Iterables.Select(columns, new Select<Column, String>()
{
public String select(Column column)
{
return column.getString1();
}
}));
}

private static void method2(Iterable<String> names)
{
for (String name : names)
{
System.out.println(name);
}
}

}