How do I print my Java object without getting "SomeType@2f92e0f4"?

Question

I have a class defined as follows:

public class Person {
  private String name;

  // constructor and getter/setter omitted
}

I tried to print an instance of my class:

System.out.println(myPerson);

but I got the following output: com.foo.Person@2f92e0f4.

A similar thing happened when I tried to print an array of Person objects:

Person[] people = //...
System.out.println(people); 

I got the output: [Lcom.foo.Person;@28a418fc

What does this output mean? How do I change this output so it contains the name of my person? And how do I print collections of my objects?

_{Note: this is intended as a canonical Q&A about this subject.}

Solution 1

Background

All Java objects have a toString() method, which is invoked when you try to print the object.

System.out.println(myObject);  // invokes myObject.toString()

This method is defined in the Object class (the superclass of all Java objects). The Object.toString() method returns a fairly ugly looking string, composed of the name of the class, an @ symbol and the hashcode of the object in hexadecimal. The code for this looks like:

// Code of Object.toString()
public String toString() {
    return getClass().getName() + "@" + Integer.toHexString(hashCode());
}

A result such as com.foo.MyType@2f92e0f4 can therefore be explained as:

• com.foo.MyType - the name of the class, i.e. the class is MyType in the package com.foo.
• @ - joins the string together
• 2f92e0f4 the hashcode of the object.

The name of array classes look a little different, which is explained well in the Javadocs for Class.getName(). For instance, [Ljava.lang.String means:

• [ - an single-dimensional array (as opposed to [[ or [[[ etc.)
• L - the array contains a class or interface
• java.lang.String - the type of objects in the array

---

Customizing the Output

To print something different when you call System.out.println(myObject), you must override the toString() method in your own class. Here's a simple example:

public class Person {

  private String name;
  
  // constructors and other methods omitted
  
  @Override
  public String toString() {
    return name;
  }
}

Now if we print a Person, we see their name rather than com.foo.Person@12345678.

Bear in mind that toString() is just one way for an object to be converted to a string. Typically this output should fully describe your object in a clear and concise manner. A better toString() for our Person class might be:

@Override
public String toString() {
  return getClass().getSimpleName() + "[name=" + name + "]";
}

Which would print, e.g., Person[name=Henry]. That's a really useful piece of data for debugging/testing.

If you want to focus on just one aspect of your object or include a lot of jazzy formatting, you might be better to define a separate method instead, e.g. String toElegantReport() {...}.

---

Auto-generating the Output

Many IDEs offer support for auto-generating a toString() method, based on the fields in the class. See docs for Eclipse and IntelliJ, for example.

Several popular Java libraries offer this feature as well. Some examples include:

• ToStringBuilder from Apache Commons Lang

• MoreObjects.ToStringHelper from Google Guava

• @ToString annotation from Project Lombok

---

Printing groups of objects

So you've created a nice toString() for your class. What happens if that class is placed into an array or a collection?

Arrays

If you have an array of objects, you can call Arrays.toString() to produce a simple representation of the contents of the array. For instance, consider this array of Person objects:

Person[] people = { new Person("Fred"), new Person("Mike") };
System.out.println(Arrays.toString(people));

// Prints: [Fred, Mike]

Note: this is a call to a static method called toString() in the Arrays class, which is different to what we've been discussing above.

If you have a multi-dimensional array, you can use Arrays.deepToString() to achieve the same sort of output.

Collections

Most collections will produce a pretty output based on calling .toString() on every element.

List<Person> people = new ArrayList<>();
people.add(new Person("Alice"));
people.add(new Person("Bob"));    
System.out.println(people);

// Prints [Alice, Bob]

So you just need to ensure your list elements define a nice toString() as discussed above.

Solution 2

I think apache provides a better util class which provides a function to get the string

ReflectionToStringBuilder.toString(object)

Solution 3

Every class in Java has the toString() method in it by default, which is called if you pass some object of that class to System.out.println(). By default, this call returns the className@hashcode of that object.

{
    SomeClass sc = new SomeClass();
    // Class @ followed by hashcode of object in Hexadecimal
    System.out.println(sc);
}

You can override the toString method of a class to get different output. See this example

class A {
    String s = "I am just a object";
    @Override
    public String toString()
    {
        return s;
    }
}

class B {
    public static void main(String args[])
    {
        A obj = new A();
        System.out.println(obj);
    }
}

Solution 4

In Eclipse, Go to your class, Right click->source->Generate toString();

It will override the toString() method and will print the object of that class.

Solution 5

I prefer to use a utility function which uses GSON to de-serialize the Java object into JSON string.

/**
 * This class provides basic/common functionalities to be applied on Java Objects.
 */
public final class ObjectUtils {

    private static final Gson GSON = new GsonBuilder().setPrettyPrinting().create();

    private ObjectUtils() {
         throw new UnsupportedOperationException("Instantiation of this class is not permitted in case you are using reflection.");
    }

    /**
     * This method is responsible for de-serializing the Java Object into Json String.
     *
     * @param object Object to be de-serialized.
     * @return String
     */
    public static String deserializeObjectToString(final Object object) {
        return GSON.toJson(object);
    }
}

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