This post is similar to Overriding equals method in Java. Consider the following Java program:
// file name: Main.java
class Complex {
private double re, im;
public Complex(double re, double im) {
this.re = re;
this.im = im;
}
}
// Driver class to test the Complex class
public class Main {
public static void main(String[] args) {
Complex c1 = new Complex(10, 15);
System.out.println(c1);
}
}
Output:
Complex@19821f
The output is, class name, then ‘at’ sign, and at the end hashCode of object. All classes in Java inherit from the Object class, directly or indirectly (See point 1 of this). The Object class has some basic methods like clone(), toString(), equals(),.. etc. The default toString() method in Object prints “class name @ hash code”. We can override toString() method in our class to print proper output. For example, in the following code toString() is overridden to print “Real + i Imag” form.
// file name: Main.java
class Complex {
private double re, im;
public Complex(double re, double im) {
this.re = re;
this.im = im;
}
/* Returns the string representation of this Complex number.
The format of string is "Re + iIm" where Re is real part
and Im is imagenary part.*/
@Override
public String toString() {
return String.format(re + " + i" + im);
}
}
// Driver class to test the Complex class
public class Main {
public static void main(String[] args) {
Complex c1 = new Complex(10, 15);
System.out.println(c1);
}
}
Output:
10.0 + i15.0
In general, it is a good idea to override toString() as we get get proper output when an object is used in print() or println().