Java equals() and hashCode() implementation example

Author: Pankaj Kumar

CoreJavaProjects/Java-Equals-Hashcode/pom.xml

@@ -0,0 +1,22 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<groupId>com.journaldev.java</groupId>
+	<artifactId>Java-Equals-Hashcode</artifactId>
+	<version>0.0.1-SNAPSHOT</version>
+
+	<build>
+		<plugins>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-compiler-plugin</artifactId>
+				<version>3.7.0</version>
+				<configuration>
+					<release>10</release>
+				</configuration>
+			</plugin>
+		</plugins>
+	</build>
+
+</project>

CoreJavaProjects/Java-Equals-Hashcode/src/main/java/com/journaldev/java/DataKey.java

@@ -0,0 +1,57 @@
+package com.journaldev.java;
+
+public class DataKey {
+
+	private String name;
+	private int id;
+
+	public String getName() {
+		return name;
+	}
+
+	public void setName(String name) {
+		this.name = name;
+	}
+
+	public int getId() {
+		return id;
+	}
+
+	public void setId(int id) {
+		this.id = id;
+	}
+
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = 1;
+		result = prime * result + id;
+		result = prime * result + ((name == null) ? 0 : name.hashCode());
+		return result;
+	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj)
+			return true;
+		if (obj == null)
+			return false;
+		if (getClass() != obj.getClass())
+			return false;
+		DataKey other = (DataKey) obj;
+		if (id != other.id)
+			return false;
+		if (name == null) {
+			if (other.name != null)
+				return false;
+		} else if (!name.equals(other.name))
+			return false;
+		return true;
+	}
+
+	@Override
+	public String toString() {
+		return "DataKey [name=" + name + ", id=" + id + "]";
+	}
+
+}

CoreJavaProjects/Java-Equals-Hashcode/src/main/java/com/journaldev/java/HashingTest.java

@@ -0,0 +1,34 @@
+package com.journaldev.java;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class HashingTest {
+
+	public static void main(String[] args) {
+		Map<DataKey, Integer> hm = getAllData();
+
+		DataKey dk = new DataKey();
+		dk.setId(1);
+		dk.setName("Pankaj");
+		System.out.println(dk.hashCode());
+
+		Integer value = hm.get(dk);
+
+		System.out.println(value);
+
+	}
+
+	private static Map<DataKey, Integer> getAllData() {
+		Map<DataKey, Integer> hm = new HashMap<>();
+
+		DataKey dk = new DataKey();
+		dk.setId(1);
+		dk.setName("Pankaj");
+		System.out.println(dk.hashCode());
+		hm.put(dk, 10);
+
+		return hm;
+	}
+
+}