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);