Java Map replaceAll() Example
February 14, 2020
replaceAll is the default method of java.util.Map and has been introduced in Java 8. The replaceAll method accepts BiFunction as an argument. The replaceAll method replaces each entry value with the result of invoking given function on that entry. The replaceAll works for each entry of the Map or it stops if specified function throws exception for any entry. Find the method declaration from Java doc.
default void replaceAll(BiFunction<? super K,? super V,? extends V> function)
BiFunction that will apply to each entry of the Map.
Example-1
In this example, we are usingHashMap.
ReplaceAll1.java
import java.util.HashMap;
import java.util.Map;
public class ReplaceAll1 {
public static void main(String[] args) {
Map<Integer, String> studentMap = new HashMap<>();
studentMap.put(101, "Mahesh");
studentMap.put(102, "Suresh");
studentMap.put(103, "Krishna");
System.out.println("--- before replaceAll() ---");
System.out.println(studentMap);
studentMap.replaceAll((k,v) -> v + "-" + k);
System.out.println("--- after replaceAll() ---");
System.out.println(studentMap);
}
}
--- before replaceAll() ---
{101=Mahesh, 102=Suresh, 103=Krishna}
--- after replaceAll() ---
{101=Mahesh-101, 102=Suresh-102, 103=Krishna-103}
Map with Map.Entry.
MapEntryTest.java
import java.util.HashMap;
import java.util.Map;
import java.util.function.BiFunction;
public class MapEntryTest {
public static void main(String[] args) {
Map<Integer, String> studentMap = new HashMap<>();
studentMap.put(101, "Mahesh");
studentMap.put(102, "Suresh");
studentMap.put(103, "Krishna");
System.out.println("--- before replaceAll() ---");
System.out.println(studentMap);
BiFunction<Integer, String, String> function = (k, v) -> v + "-" + k;
for (Map.Entry<Integer, String> entry : studentMap.entrySet())
entry.setValue(function.apply(entry.getKey(), entry.getValue()));
System.out.println("--- after replaceAll() ---");
System.out.println(studentMap);
}
}
--- before replaceAll() ---
{101=Mahesh, 102=Suresh, 103=Krishna}
--- after replaceAll() ---
{101=Mahesh-101, 102=Suresh-102, 103=Krishna-103}
Example-2
Find one more example usingHashMap.
ReplaceAll2.java
import java.util.HashMap;
import java.util.Map;
public class ReplaceAll2 {
public static void main(String[] args) {
Map<Integer, String> studentMap = new HashMap<>();
studentMap.put(101, "Mahesh");
studentMap.put(102, "Suresh");
studentMap.put(103, "Krishna");
System.out.println("--- before replaceAll() ---");
System.out.println(studentMap);
studentMap.replaceAll((k,v) -> {
if (k == 102) {
return v + "-" + k;
}
return v;
});
System.out.println("--- after replaceAll() ---");
System.out.println(studentMap);
}
}
--- before replaceAll() ---
{101=Mahesh, 102=Suresh, 103=Krishna}
--- after replaceAll() ---
{101=Mahesh, 102=Suresh-102, 103=Krishna}
Example-3
In this example, we are usingLinkedHashMap.
ReplaceAll3.java
import java.util.LinkedHashMap;
import java.util.Map;
public class ReplaceAll3 {
public static void main(String[] args) {
Map<Integer, Integer> numberMap = new LinkedHashMap<>();
numberMap.put(1, 100);
numberMap.put(2, 200);
numberMap.put(3, 300);
System.out.println("--- before replaceAll() ---");
System.out.println(numberMap);
numberMap.replaceAll((k, v) -> v * k);
System.out.println("--- after replaceAll() ---");
System.out.println(numberMap);
}
}
--- before replaceAll() ---
{1=100, 2=200, 3=300}
--- after replaceAll() ---
{1=100, 2=400, 3=900}
Example-4
In this example, we are usingTreeMap.
ReplaceAll4.java
import java.util.Map;
import java.util.TreeMap;
public class ReplaceAll4 {
public static void main(String[] args) {
Map<String, String> treeMap = new TreeMap<>();
treeMap.put("Bharat", "Modi");
treeMap.put("Russia", "Putin");
treeMap.put("USA", "Trump");
System.out.println("--- before replaceAll() ---");
System.out.println(treeMap);
treeMap.replaceAll((k, v) -> "Mr. "+ v);
System.out.println("--- after replaceAll() ---");
System.out.println(treeMap);
}
}
--- before replaceAll() ---
{Bharat=Modi, Russia=Putin, USA=Trump}
--- after replaceAll() ---
{Bharat=Mr. Modi, Russia=Mr. Putin, USA=Mr. Trump}
