Replace and Replace All

Certain times the single entire value or the entire value of the map needs to be updated, in the case of a single update, the traditional way is to get the value based on the key or for the entire value, iterate the whole Map over the entry set and update each entry.

package org.wesome.java8;

import java.util.HashMap;
import java.util.Map;
import java.util.Objects;

class Apple {
    public static void main(String[] args) {

        Map<Integer, String> map = new HashMap<>();
        map.put(1, "Macintosh");
        map.put(2, "Fuji");
        map.put(3, "Gala");
        map.put(4, "Jonagold");

        String temp = map.get(1);
        if (Objects.nonNull(temp) && temp.equals("Macintosh")) {
            map.put(1, "MACINTOSH");
        }

        for (Map.Entry<Integer, String> entry : map.entrySet()) {
            entry.setValue(entry.getValue().concat(" Apple"));
        }

        System.out.println("map = " + map);
    }
}

to avoid the boilerplate iteration loop, Java 8 introduced the replaceAll method in Map Interface, it internally iterates over the map and updates the value corresponding to each key.

replaceAll method will modify the entire existing Map

The replaceAll method will be available for all Map Intertface implementing concrete classes such as HashMap, LinkedHashMap and TreeMap ect

package org.wesome.java8;

import java.util.HashMap;
import java.util.Map;
import java.util.function.BiFunction;

class Apple {
    public static void main(String[] args) {
        BiFunction<Integer, String, String> biFunction = (key, value) -> value + " Apple";

        Map<Integer, String> map = new HashMap<>();
        map.put(1, "Macintosh");
        map.put(2, "Fuji");
        map.put(3, "Gala");
        map.put(4, "Jonagold");
        /*  Replace a single entry, if key is present and has the old value, then update with the new value */
        map.replace(1, "Macintosh", "MACINTOSH");

        System.out.println("map = " + map);

        /*  Replace all the entry with the new value using lambda expression    */
        map.replaceAll((key, val) -> val + " Apple");

        System.out.println("map = " + map);

        /*  Replace all the entry with the new value using BiFunction  */
        map.replaceAll(biFunction);

        System.out.println("map = " + map);
    }
}