Defining a String Representation

Python

Java

The str function converts any object to its string representation.

Example:

str(3.14) # returns '3.14'

This function can be customized to return the appropriate string for objects of any programmer-defined class by including an __str__ method.

When the __str__ method is available, operations such as print automatically use it to obtain an object’s string representation.

Example:

class Student:

NUM_GRADES = 5

def __init__(self, name):

self.name = name

self.grades = []

for i in range(Student.NUM_GRADES):

self.grades.append(0)

def __str__(self):

"""Format: Name on the first line

and all grades on the second line,

separated by spaces.

"""

result = self.name + '\n'

result += ''.join(map(str, self.grades))

return result

Usage:

s1 = Student('Mary')

print(s1)

s2 = Student('Bill')

print(str(s1) + '\n' + str(s2))

The toString() method returns the string representation of an object. A default implementation of this method is included in the Object class. This implementation returns a string containing the name of the object’s class and its hash code. Thus, if the programmer does not include toString in a given class, the default is used via inheritance (Object is the ancestor class of all objects).

Operations such as println and + automatically call toString with objects to obtain their string representations.

The header of toString is

public String toString()

Example:

public class Student{

public static final int NUM_GRADES = 5;

private String name;

private int[] grades;

public Student(String name){

this.name = name;

this.grades = new int[NUM_GRADES];

}

public String toString(){

Format: Name on the first line

and all grades on the second line,

separated by spaces.

String result = this.name + '\n';

for (String grade : this.grades)

result += grade + ' ';

return result;

}

Usage:

s1 = new Student("Mary");

System.out.println(s1);

s2 = new Student("Bill");

System.out.println(s1 + '\n' + s2);

Index