Print the Default Value When Overriding toString() Method

1. Introduction

We can use the toString() method in Java to return a string representation of an object. Often, it’s overridden to provide a meaningful description of the object’s state. However, certain fields might be null, and printing them could lead to NullPointerExceptions.

In this tutorial, we’ll explore several approaches to handling this scenario by using default values.

2. An Employee Use Case Scenario

Let’s consider that we develop an application that manages employee records. Each employee has attributes such as name, age, and department:

public class Employee {
    private String name;
    private int age;
    private String department;
    public Employee(String name, int age, String department) {
        this.name = name;
        this.age = age;
        this.department = department;
    }
}

In addition, it’s crucial to clearly and informatively represent each Employee object when displaying employee information.

However, in real-world scenarios, an employee’s name and department attributes may sometimes be null, leading to unexpected behavior if not appropriately handled.

3. Null Check within the toString() Method

One of the simplest approaches is to perform a null check within the toString() method for each field that could potentially be null. If the field is null, we can print a default value instead. Here’s a basic example:

@Override
public String toString() {
    return "Name: " + (name != null ? name : "Unknown") +
      ", Age: " + age +
      ", Department: " + (department != null ? department : "Unknown");
}

In this approach, when a name or department is null, we print “Unknown” instead to prevent displaying null values in the string representation of the Employee object.

4. Using the Optional Class

Java 8 introduced the Optional class, which can be utilized to handle null values more elegantly.

Here’s how it can be done:

@Override
public String toString() {
    return "Name: " + Optional.ofNullable(name).orElse("Unknown") +
      ", Age: " + age +
      ", Department: " + Optional.ofNullable(department).orElse("Unknown");
}

If the name or department is null, we print “Unknown” instead of null using the Optional’s orElse() method.

5. Custom Helper Method

Creating a custom helper method can improve code readability, especially if multiple fields need to be checked for null values. Additionally, this method can encapsulate the null check and default value assignment logic.

Here’s an example:

private String getDefaultIfNull(String value, String defaultValue) {
    return value != null ? value : defaultValue;
}

Here, we create a custom helper method getDefaultIfNull() to handle null values. This method checks if the value is null and returns the default value if it is.

Then, within the toString() method, we utilize the getDefaultIfNull() method to handle null values for each field:

@Override
public String toString() {
    return "Name: " + getDefaultIfNull(name, "Unknown") +
      ", Age: " + age +
      ", Department: " + getDefaultIfNull(department, "Unknown");
}

6. Using the Objects.toString() Method

Java provides a utility method Objects.toString() to handle null values when converting objects to strings:

@Override
public String toString() {
    return "Name: " + Objects.toString(name, "Unknown") +
      ", Age: " + age +
      ", Department: " + Objects.toString(department, "Unknown");
}

In this approach, we utilize the Objects.toString() method to print “Unknown” instead of null if the name or department fields are null.

7. Conclusion

In this article, we discussed overriding the toString() method and handling the potential null within.

As always, the complete code samples for this article can be found over on GitHub.