Override equals() in Java

Question

I am attempting to understand how "equals()" works in Java. Especially in contrast to "toString()". Here is an example that is throwing me off course.

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public class Car
{
    String make, model;

    public Car( String model, String make )
    {
        this.make  = model;
        this.model = make;
    }   

    public String toString()
    {
        String str = "This is a car. ";
        str += "Make: " + make + " | Model: " + model;
        return str;
    }

    public boolean equals( Car c )
    {
        return ( make.equals( c.make ) && model.equals( c.model ) );
    }
}

---

public class Node 
{
    protected Object obj;
    protected Node next;

    public Node( Object o )
    {
        this.obj = o;
        this.next = null;
    }

    public String toString()
    {
        return obj.toString();
    }

    public boolean equals( Node n )
    {
        return ( this.obj.equals( n.obj ) );
    }
}

---

Car c1 = new Car("toyota", "corolla");
Car c2 = new Car("toyota", "corolla");

Node nC1 = new Node( c1 );
Node nC2 = new Node( c2 );

nC1.print();
nC2.print();


if( nC1.equals( nC2 ) )
    System.out.println("They are equal!");
else
    System.out.println("They are NOT equal!");

---

Here nC1.print() and nC2.print() behaves as expected. Prints:

This is a car. Make: toyota | Model: corolla
This is a car. Make: toyota | Model: corolla

However nC1.equals( nC2 ), prints:

"They are NOT equal!"

In short the question is that I can override "toString()", but not "equals()". What am I missing? I presume there is a simple explanation for this behavior.

Answer 1

I think you should keep the signature of the method as:

public boolean equals(Object obj)

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As a side note: put @Override annotation within the method you want to override to make sure that you are overriding the right method, otherwise the compiler complains.