Equals / HashCode / ToString template

equals-hashcode-tostring.java

import java.util.Objects;

/*
 * When defining equals, hashCode should be defined too.
 * It is the civil thing to define toString too.
 */

class Base {
	public String a = "a";
	
	@Override
	public boolean equals(Object obj) {
		if (obj == null) { return false; }
		if (obj == this) { return true; }
		if (getClass() != obj.getClass()) { return false; }
		Base other = (Base) obj;
		return Objects.equals(this.a, other.a);
	}
	
	@Override
	public int hashCode() {
		return Objects.hash(this.a);
	}
	
	@Override
	public String toString() {
		return getClass().getName() + "[a=" + a + "]";
	}
}

class Super extends Base {
	public String b = "b";

	@Override
	public boolean equals(Object obj) {
		if (! super.equals(obj)) { return false; }
		Super other = (Super) obj;
		return Objects.equals(this.b, other.b);
	}
	
	@Override
	public int hashCode() {
		return Objects.hash(super.hashCode(), this.b);
	}
	
	@Override
	public String toString() {
		return super.toString() + "[b=" + b + "]";
	}
}

public class Sandbox {
	public static void main(String[] args) {
		Base b = new Base();
		Super s = new Super();
		System.out.println(b);
		System.out.println(s);
	}

}