Show how to use instanceof to implement equals

Author: Nicolai Parlog

src/main/java/org/codefx/demo/java16/lang/instanceof_/Equals.java

@@ -0,0 +1,35 @@
+package org.codefx.demo.java16.lang.instanceof_;
+
+import java.util.Objects;
+
+import static java.util.Objects.requireNonNull;
+
+/**
+ * Pattern matching in {@code if} works great for implementing {@code equals}.
+ */
+public class Equals {
+
+	private final String someField;
+	private final String anotherField;
+
+	public Equals(String someField, String anotherField) {
+		this.someField = requireNonNull(someField);
+		this.anotherField = requireNonNull(anotherField);
+	}
+
+	@Override
+	// note that an `equals` implementation that uses `instanceof`,
+	// should be final to prevent subclasses from overriding it,
+	// which usually breaks symmetry or transitivity
+	public final boolean equals(Object o) {
+		return o instanceof Equals other
+				&& someField.equals(other.someField)
+				&& anotherField.equals(other.anotherField);
+	}
+
+	@Override
+	public int hashCode() {
+		return Objects.hash(someField, anotherField);
+	}
+
+}