JDBC with lambda, Java

JDBC with lambda

//'main' method must be in a class 'Rextester'.
//Compiler version 1.8.0_72

import java.util.*;
import java.lang.*;
import java.time.*;

class Rextester
{  
    public static void main(String args[])
    {
        Rextester tester = new Rextester();
        tester.test1();
        tester.test2();
        tester.test3();
        tester.test4();
        tester.test5();
        tester.test6();
    }
    
    public void test1() {
        List<String> strList = getColumnValuesAsList("WORK_ORDERS", "WORK_ORDER_ID", "WHERE ROWNUM < 10", String.class, (rs, list) -> {
            list.add(rs.getString());
            return list;
        });
        System.out.println(strList);
    }
    
    public void test2() {
        List<Integer> intList = getColumnValuesAsList("WORK_ORDERS", "WORK_ORDER_ID", "WHERE ROWNUM < 10", Integer.class, (rs, list) -> {
            list.add(rs.getInt());
            return list;
        });
        System.out.println(intList);
    }
    
    public void test3() {
        List<Long> longList = getColumnValuesAsList("WORK_ORDERS", "WORK_ORDER_ID", "WHERE ROWNUM < 10", Long.class, (rs, list) -> {
            list.add(rs.getLong());
            return list;
        });
        System.out.println(longList);
    }
    
    public void test4() {
        List<Float> floatList = getColumnValuesAsList("WORK_ORDERS", "WORK_ORDER_ID", "WHERE ROWNUM < 10", Float.class, (rs, list) -> {
            list.add(rs.getFloat());
            return list;
        });
        System.out.println(floatList);
    }
    
    public void test5() {
        List<Double> doubleList = getColumnValuesAsList("WORK_ORDERS", "WORK_ORDER_ID", "WHERE ROWNUM < 10", Double.class, (rs, list) -> {
            list.add(rs.getDouble());
            return list;
        });
        System.out.println(doubleList);
    }
    
    public void test6() {
        List<Date> dateList = getColumnValuesAsList("WORK_ORDERS", "WORK_ORDER_ID", "WHERE ROWNUM < 10", Date.class, (rs, list) -> {
            list.add(rs.getDate());
            return list;
        });
        System.out.println(dateList);
    }
    
    @FunctionalInterface
    public interface ResultSetProcessor<T> {
        public List<T> getResultToList(RS rs, List<T> list);
    }
    
    public <T> List<T> getColumnValuesAsList(String table, String column, String whereClause, Class<T> clazz, ResultSetProcessor<T> processor) {
        List<T> list = new ArrayList<>();
        String query = "SELECT " + column + " FROM " + table + " " + whereClause; // dummy. not used
        RS rs = new RS(10);
        while(rs.next()) {
            list = processor.getResultToList(rs, list);
        }
        return list;
    }
    
    public class RS {
        int value = 0;
        int max = 0;
        
        public RS(int max) {
            this.max = max;
        }
        
        public boolean next() {
            return value++ < max;
        }
        
        public String getString() {
            return "\"" + value + "\"";
        }
        
        public int getInt() {
            return value;
        }
        
        public long getLong() {
            return 10000000000L + (long)value;
        }
        
        public float getFloat() {
            return 0.1f * value;
        }
        
        public double getDouble() {
            return 0.00000000000001 * value;
        }
        
        public Date getDate() {
            return Calendar.getInstance().getTime();
        }
    }
            
}


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