WriteToExcel

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

public class ToExcel {
    static interface WritableToExcel {
        public int getCellCount();
        public String getCellData(int cell);
    }

    static class Employee implements WritableToExcel {
        private String name;
        private int pay;

        public Employee(String name, int pay) {
            this.name = name;
            this.pay = pay;
        }

        @Override
        public int getCellCount() {
            return 2;
        }

        @Override
        public String getCellData(int cell) {
            if(cell == 0) {
                return name;
            }
            if (cell == 1) {
                return pay + "";
            }
            return null;
        }

    }

    static class ObejctTest implements WritableToExcel {
        private String foo, boo, bar;

        public ObejctTest(String foo, String boo, String bar) {
            this.foo = foo;
            this.boo = boo;
            this.bar = bar;
        }

        @Override
        public int getCellCount() {
            return 3;
        }

        @Override
        public String getCellData(int cell) {
            switch(cell) {
                case 0: return foo;
                case 1: return boo;
                case 2: return bar;
                default: return null;
            }
        }
    }

    public static void main(String[] args) {
        List<Employee> emp = new ArrayList<>();
        emp.add(new Employee("Frank", 500));
        emp.add(new Employee("Ben", 600));
        emp.add(new Employee("Alice", 550));

        List<ObejctTest> obj = new ArrayList<>();
        obj.add(new ObejctTest("one", "two", "three"));
        obj.add(new ObejctTest("red", "green", "blue"));

        writeReportToExcel(emp, obj);
    }

    static void writeReportToExcel(List<? extends WritableToExcel>... lists) {
        //not really write to excel, but to stdout
        for(List<? extends WritableToExcel> list: lists) {
            System.out.println("New list");
            for(WritableToExcel element: list) {
                for(int i = 0; i<element.getCellCount(); i++) {
                    System.out.print(element.getCellData(i) +", ");
                }
                System.out.println();
            }
        }
    }
}

/*
OUTPUT:
New list
Frank, 500,
Ben, 600,
Alice, 550,
New list
one, two, three,
red, green, blue,
*/