BAEL 5414 - Java null check why use == instead of .equals() (#12124)

core-java-modules/core-java-lang-5/README.md

@@ -0,0 +1,5 @@
+## Core Java Lang (Part 5)
+
+This module contains articles about core features in the Java language
+
+## TODO ##

core-java-modules/core-java-lang-5/pom.xml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<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>
+    <artifactId>core-java-lang-5</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-lang-5</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+
+    <build>
+        <finalName>core-java-lang-5</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+</project>

core-java-modules/core-java-lang-5/src/test/java/com/baeldung/nullchecks/NullChecksUnitTest.java

@@ -0,0 +1,125 @@
+package com.baeldung.nullchecks;
+
+import org.junit.Test;
+
+import java.util.Objects;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class NullChecksUnitTest {
+
+    @Test
+    public void whenReferenceEqualityOnPrimitives_thenCompareValues() {
+        int a = 10;
+        int b = 15;
+        int c = 10;
+        int d = a;
+
+        // different values check
+        assertFalse(a == b);
+
+        // same values check
+        assertTrue(a == c);
+
+        // same references check
+        assertTrue(a == d);
+    }
+
+    @Test
+    public void whenReferenceEqualityOnObjects_thenCompareReferences() {
+        Person a = new Person("Bob", 20);
+        Person b = new Person("Mike", 40);
+        Person c = new Person("Bob", 20);
+        Person d = a;
+        Person e = null;
+
+        // different values check
+        assertFalse(a == b);
+
+        // same values check
+        assertFalse(a == c);
+
+        // same references check
+        assertTrue(a == d);
+
+        // same references check - for nulls
+        assertTrue(e == null);
+    }
+
+    @Test
+    public void whenValueEqualityOnPrimitives_thenCompareValues() {
+        int a = 10;
+        Integer b = a;
+
+        assertTrue(b.equals(10));
+    }
+
+    @Test
+    public void whenValueEqualityOnObjects_thenCompareValues() {
+        Person a = new Person("Bob", 20);
+        Person b = new Person("Mike", 40);
+        Person c = new Person("Bob", 20);
+        Person d = a;
+        Person e = null;
+
+        // different values check
+        assertFalse(a.equals(b));
+
+        // same values check
+        assertTrue(a.equals(c));
+
+        // same references check
+        assertTrue(a.equals(d));
+
+        // null checks
+        assertFalse(a.equals(e));
+        assertThrows(NullPointerException.class, () -> e.equals(a));
+
+        // null checks fixed
+        assertFalse(e != null && e.equals(a));
+
+        // using Objects.equals
+        assertFalse(Objects.equals(e, a));
+        assertTrue(Objects.equals(null, e));
+
+    }
+
+    private class Person {
+        private String name;
+        private int age;
+
+        public Person(String name, int age) {
+            this.name = name;
+            this.age = age;
+        }
+
+        public String getName() {
+            return name;
+        }
+
+        public void setName(String name) {
+            this.name = name;
+        }
+
+        public int getAge() {
+            return age;
+        }
+
+        public void setAge(int age) {
+            this.age = age;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) return true;
+            if (o == null || getClass() != o.getClass()) return false;
+            Person person = (Person) o;
+            return age == person.age && Objects.equals(name, person.name);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(name, age);
+        }
+    }
+}

core-java-modules/pom.xml

@@ -73,6 +73,7 @@
         <module>core-java-lang-2</module>
         <module>core-java-lang-3</module>
         <module>core-java-lang-4</module>
+        <module>core-java-lang-5</module>
         <module>core-java-lang-math</module>
         <module>core-java-lang-math-2</module>
         <module>core-java-lang-math-3</module>