equals(), hashCode(), and toString()

Syntax

@Override\npublic boolean equals(Object o) { }\n@Override\npublic int hashCode() { }\n@Override\npublic String toString() { }

Examples

class Point {
    int x, y;
    Point(int x, int y) { this.x = x; this.y = y; }
}

Point p1 = new Point(3, 4);
Point p2 = new Point(3, 4);

System.out.println(p1 == p2);        // false - different objects
System.out.println(p1.equals(p2));   // false - default equals() is the same as ==
System.out.println(p1);               // Point@1b6d3586 - unreadable default toString()

class Point {
    int x, y;
    Point(int x, int y) { this.x = x; this.y = y; }

    @Override
    public String toString() {
        return "Point(" + x + ", " + y + ")";
    }
}

Point p = new Point(3, 4);
System.out.println(p);  // Point(3, 4) - much more useful for debugging

import java.util.Objects;

class Point {
    int x, y;
    Point(int x, int y) { this.x = x; this.y = y; }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Point)) return false;
        Point other = (Point) o;
        return x == other.x && y == other.y;
    }

    @Override
    public int hashCode() {
        return Objects.hash(x, y);
    }
}

Point p1 = new Point(3, 4);
Point p2 = new Point(3, 4);
System.out.println(p1.equals(p2));  // true - compares field values now

java.util.Set<Point> points = new java.util.HashSet<>();
points.add(p1);
System.out.println(points.contains(p2));  // true - relies on both equals() AND hashCode()

Best practices

• Always override equals() and hashCode() together - overriding just one breaks the contract that equal objects must have equal hash codes
• Use java.util.Objects.hash(field1, field2, ...) for a quick, reliable hashCode() implementation instead of writing the hashing logic by hand
• Override toString() on any class you plan to log or print for debugging - the default output is not useful
• Consider a record instead of a manual class when all you need is a simple immutable value type - it generates all three methods correctly for you

At a glance

Purpose

General-purpose application development

File extension

.java

Runs in

Java Virtual Machine

Usually used with

JDK and Java libraries

Specifications & further reading

• Java Language Specification

Related Java documentation