/* package whatever; // don't place package name! */

import java.math.BigDecimal;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.function.Function;

class Ideone {
    public static void main(String[] args) {
        MyRow row1 = new MyRow(BigDecimal.ONE);
        MyRow row2 = new MyRow(BigDecimal.TEN);
        List<MyRow> rows = Arrays.asList(row1, row2);

        rows.stream().map(x -> x.getValue()).reduce(BigDecimal.ZERO, BigDecimal::add);
        //calcSum(rows, (MyRow x) -> x.getValue());
    }

    public static BigDecimal calcSum(Collection c , Function<?, BigDecimal> mapFunc) {
        return c.stream().map(mapFunc).reduce(BigDecimal.ZERO, BigDecimal::add);
    }
    
}

class MyRow {
    private BigDecimal value;

    public MyRow(BigDecimal value) {
        this.value = value;
    }

    public BigDecimal getValue() {
        return value;
    }

    public void setValue(BigDecimal value) {
        this.value = value;
    }
}