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.}

Answer 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

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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() {...}.

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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

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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.

Answer 2

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

ReflectionToStringBuilder.toString(object)