Almost every class in Java is a direct or indirect subclass of java.lang.Object. Understanding this root class—and the methods it provides—is key to mastering how Java objects behave and interact.

Everything you create in Java—unless you explicitly extend another class—automatically gets these methods. Let’s look at the most important ones and why they matter.

toString() Returns a string that “represents” the object. By default, it prints the class name and hash code, but you almost always override it for readability.

@Override
public String toString() {
    return "Person[name=" + name + ", age=" + age + "]";
}

Without override: Person@5e2de80c With override: Person[name=Arun, age=30]

equals(Object other) Tests whether this object is “equal” to another. The default is reference equality (this == other), so you override it to compare data instead.

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (!(o instanceof Person)) return false;
    Person p = (Person) o;
    return age == p.age && Objects.equals(name, p.name);
}

When you override equals(), you almost always override hashCode() too.

hashCode() Returns an integer hash code for the object, used in hash-based collections. Objects that are equal must have the same hash code.

@Override
public int hashCode() {
    return Objects.hash(name, age);
}

Good hashCode() implementations distribute values uniformly to avoid collisions.

getClass() Returns a Class<?> object representing the runtime class of the instance. Useful for reflection or debugging.

System.out.println(obj.getClass().getName());

clone() Creates and returns a copy of the object. The class must implement Cloneable, and override clone() with protected Object clone() throws CloneNotSupportedException.

@Override
public Person clone() throws CloneNotSupportedException {
    return (Person) super.clone();
}

Because cloning is tricky, many prefer copy constructors or factory methods instead.

finalize() (deprecated) Called by the garbage collector before reclaiming an object’s memory. It’s unpredictable, often dangerous, and deprecated in modern Java. Instead, use try-with-resources or explicit cleanup methods.

Threading Helpers: wait(), notify(), notifyAll() Since every object has a monitor, these methods let threads coordinate:

synchronized (shared) {
    while (!condition) {
        shared.wait();
    }
    // ...
    shared.notifyAll();
}

Use higher-level constructs (Lock, Condition, Semaphore) from java.util.concurrent for complex scenarios.

• Consistent APIs: Any object can be printed, compared, cloned, or used in synchronized blocks.
• Collections: equals() and hashCode() are the backbone of Set, Map, and other data structures.
• Debugging: A good toString() makes logs and error messages far more informative.
• Concurrency: The built-in monitor model is simple but limited—knowing about wait/notify helps you appreciate modern concurrency utilities.

Understanding java.lang.Object is like learning the alphabet of Java’s object model. Everything else builds on these fundamental methods.