john77eipe

//Vendor code

static class IntegerAddition implements BinaryOperator<Integer> {

	static private IntegerAddition instance = new IntegerAddition() ;
	private IntegerAddition() {}
	
	@Override
	public Integer apply(Integer t, Integer u) {
		return t + u;

john77eipe

//Vendor makes this change to utilize java 8 features but he faces this issue
public static <T extends Number> Optional<T> sum(List<T> list, Predicate<T> condition){
	//ability to add is only here
		return list.parallelStream()
		.filter(condition)
		.map(i -> i)
        .reduce((a,b)->a+b); //Compile error: Operator + is undefined for type T, T
}

//client

john77eipe

//no changes to vendor

//in client just this line of code ;-)

int result = MathUtility.sum(listOfInts, (Integer i)->{return (i<3);});

//still shorter way of doing it

int result = MathUtility.sum(listOfInts, i ->i<3);

john77eipe

interface ConditionCheck<T> {
	public boolean check(T i);
}

class MathUtility<T extends Number> {
	public static <T extends Number> Number sum(List<T> list, ConditionCheck<T> condition){
		//ability to add is only here
		
		Number sum = 0;
		for(T i: list){

john77eipe

//Vendor's code

interface ConditionCheck {
	public boolean check(Integer i);
}

class MathUtility {
	public static int sum(List<Integer> list, ConditionCheck condition){
		//ability to add is only here
		int sum=0;

john77eipe

//client creates list of Ints
List<Integer> listOfInts = new ArrayList<Integer>();
listOfInts.add(2);
listOfInts.add(3);
listOfInts.add(4);

//client does the filtering based on his logic
//let's say he wants to filter out even numbers
Iterator<Integer> itr = listOfInts.iterator();
while (itr.hasNext()) {

john77eipe

//before
Runnable r1 = new Runnable() {
  @Override
	public void run() {
	  System.out.println("My Runnable");
	}
};

//now
Runnable r2 = () -> System.out.println("My Runnable");

john77eipe

package async;

import java.io.IOException;

import javax.servlet.AsyncContext;
import javax.servlet.AsyncEvent;
import javax.servlet.AsyncListener;
import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletOutputStream;

john77eipe

package async;

import java.io.IOException;

import javax.servlet.AsyncContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

john77eipe

package async;

import java.io.IOException;

import javax.servlet.AsyncContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;