ConcretePage.comJava Map replace()
February 15, 2020
replace is the default method of java.util.Map and has been introduced in Java 8. The replace method replaces the entry value for the specified key only if it is currently mapped to some value. The replace method uses following arguments.
1. Replaces the value for the specified key.
default V replace(K key, V value)
The value is the new value to be put.
The
replace method returns old value and if there is no associated value with specified key, then it returns null.
2. Replaces the value with new value for the specified key only if the specified old value matches the value associated with specified key.
default boolean replace(K key, V oldValue, V newValue)
The oldValue is the is old value associated with specified key.
The newValue is the is new value to be put.
The
replace method returns true/false whether replacement of value is successful. If specified key has no associated value, then there is no replacement and hence will return false. If already existing old value for the specified key does not match the specified old value, there is no replacement and hence returns false.
Example-1
In this example, we are usingHashMap.
Replace1.java
import java.util.HashMap;
import java.util.Map;
public class Replace1 {
public static void main(String[] args) {
Map<Integer, String> studentMap = new HashMap<>();
studentMap.put(101, "Mahesh");
studentMap.put(102, "Suresh");
studentMap.put(103, "Krishna");
String oldValue = studentMap.replace(101, "Mr. Mahesh");
System.out.println(oldValue); //Mahesh
System.out.println(studentMap.get(101)); //Mr. Mahesh
boolean isReplaced = studentMap.replace(102, "Suresh", "Mr. Suresh");
System.out.println(isReplaced); //true
System.out.println(studentMap.get(102)); //Mr. Suresh
isReplaced = studentMap.replace(103, "Krishna11", "Mr. Krishna");
System.out.println(isReplaced); //false
System.out.println(studentMap.get(103)); //Krishna
}
}
Mahesh Mr. Mahesh true Mr. Suresh false Krishna
replace method.
Replace11.java
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
public class Replace11 {
public static void main(String[] args) {
Map<Integer, String> studentMap = new HashMap<>();
studentMap.put(101, "Mahesh");
studentMap.put(102, "Suresh");
studentMap.put(103, "Krishna");
int key1 = 101;
if (studentMap.containsKey(key1)) {
studentMap.put(key1, "Mr. Mahesh");
}
System.out.println(studentMap.get(key1));
int key2 = 102;
if (studentMap.containsKey(key2) && Objects.equals(studentMap.get(key2), "Suresh")) {
studentMap.put(102, "Mr. Suresh");
}
System.out.println(studentMap.get(key2));
}
}
Mr. Mahesh Mr. Suresh
Example-2
In this example, we are usingLinkedHashMap.
Replace2.java
import java.util.LinkedHashMap;
import java.util.Map;
public class Replace2 {
public static void main(String[] args) {
Map<Integer, Integer> numberMap = new LinkedHashMap<>();
numberMap.put(1, 100);
numberMap.put(2, 200);
numberMap.put(3, 300);
numberMap.replace(1, numberMap.get(1) + 50);
System.out.println(numberMap.get(1)); //150
numberMap.replace(2, 200, 250);
System.out.println(numberMap.get(2)); //250
numberMap.replace(3, 301, 350);
System.out.println(numberMap.get(3)); //300
}
}
150 250 300
Example-3
In this example, we are usingTreeMap.
Replace3.java
import java.util.Map;
import java.util.TreeMap;
public class Replace3 {
public static void main(String[] args) {
Map<String, String> treeMap = new TreeMap<>();
treeMap.put("Bharat", "Modi");
treeMap.put("Russia", "Putin");
treeMap.put("USA", "Trump");
String key1 = "Bharat";
treeMap.replace(key1, "Mr. Modi");
System.out.println(treeMap.get(key1)); //Mr. Modi
String key2 = "Russia";
treeMap.replace(key2, "Putin", "Mr. Putin");
System.out.println(treeMap.get(key2)); //Mr. Putin
String key3 = "USA";
treeMap.replace(key3, "", "Mr. Trump");
System.out.println(treeMap.get(key3)); //Trump
}
}
Mr. Modi Mr. Putin Trump
