By Duncan Jones


2015-03-19 08:59:18 8 Comments

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: [email protected].

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.

10 comments

@Pankaj Manali 2015-03-19 10:04:48

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 [email protected] 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);
    }
}

@gvlasov 2015-03-24 21:28:39

This is a well-put and short answer, but to clarify why OP is getting [Lcom.foo.Person;@28a418fc as output: that's the output of toString() method, too, but of the one that is implemented in the class that is generated at runtime for the type Person[], not Person (see stackoverflow.com/a/8546532/1542343).

@Pankaj Manali 2015-03-25 14:03:51

This output means [email protected] . The default toString() method has return type like. return Object.hasCode() or some similar return statement which is returning hashcode in hexadecimal form along with class name.

@Agam 2018-10-09 12:18:40

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);
    }
}

@adn.911 2017-12-02 16:23:14

By default, every Object in Java has the toString() method which outputs the [email protected]

If you want more meaningfull information then you need to override the toString() method in your class.

public class Person {
  private String name;

  // constructor and getter/setter omitted

  // overridding toString() to print name
  public String toString(){
     return name;  
  }
}

Now when you print the person object using System.out.prtinln(personObj); it will print the name of the person instead of the classname and hashcode.

In your second case when you are trying to print the array, it prints [Lcom.foo.Person;@28a418fc the Array type and it's hashcode.


If you want to print the person names, there are many ways.

You could write your own function that iterates each person and prints

void printPersonArray(Person[] persons){
    for(Person person: persons){
        System.out.println(person);
    }
}

You could print it using Arrays.toString(). This seems the simplest to me.

 System.out.println(Arrays.toString(persons));
 System.out.println(Arrays.deepToString(persons));  // for nested arrays  

You could print it the java 8 way (using streams and method reference).

 Arrays.stream(persons).forEach(System.out::println);

There might be other ways as well. Hope this helps. :)

@Ketan Keshri 2016-04-21 13:45:21

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.

@Duncan Jones 2015-03-19 08:59:18

Background

All Java objects have a toString() method, which is invoked when you try and 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 [email protected] 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 [email protected].

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:


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.

@CrandellWS 2016-05-23 05:55:23

return String.format( getClass().getSimpleName() + "[ name=%s ]", name); and really instead of name it should use the getter getName() (but getters were omitted in the Person class...) but if a getter was used ... return String.format( getClass().getSimpleName() + "[ name=%s ]", getName());

@yatinbc 2016-10-10 09:22:42

if i have two classes in java file then how to create object of class which is not public A.java public class A{ } class B{ } ------ C.java public class C{ A a = new A(); }

@Ole V.V. 2017-03-09 15:17:37

Note that there are overloaded versions of Arrays.toString() so you can use it for arrays of primitives too (int[], double[]). Also Arrays.deepToString() handles multidimensional arrays of primitives nicely.

@Hemant Thorat 2017-07-07 14:06:07

Arrays.deepToString(arrayOfObject)

Above function print array of object of different primitives.

[[AAAAA, BBBBB], [6, 12], [2003-04-01 00:00:00.0, 2003-10-01 00:00:00.0], [2003-09-30 00:00:00.0, 2004-03-31 00:00:00.0], [Interim, Interim], [2003-09-30, 2004-03-31]];

@Tim 2017-11-24 18:11:26

This only allows printing primitives, not the complex objects

@Yasir Shabbir Choudhary 2017-03-27 06:21:35

If you look at the Object class (Parent class of all classes in Java) the toString() method implementation is

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

whenever you print any object in Java then toString() will be call. Now it's up to you if you override toString() then your method will call other Object class method call.

@Mr.Q 2016-07-28 06:00:49

In intellij you can auto generate toString method by pressing alt+inset and then selecting toString() here is an out put for a test class:

public class test  {
int a;
char b;
String c;
Test2 test2;

@Override
public String toString() {
    return "test{" +
            "a=" + a +
            ", b=" + b +
            ", c='" + c + '\'' +
            ", test2=" + test2 +
            '}';
 }
}

As you can see, it generates a String by concatenating, several attributes of the class, for primitives it will print their values and for reference types it will use their class type (in this case to string method of Test2).

@Vikrant Kashyap 2016-05-06 11:22:24

If you Directly print any object of Person It will the [email protected] to the Code.

in your case [email protected] is getting printed . Where Person is a class to which object belongs and 2f92e0f4 is hashCode of the Object.

public class Person {
  private String name;

  public Person(String name){
  this.name = name;
  }
  // getter/setter omitted

   @override
   public String toString(){
        return name;
   }
}

Now if you try to Use the object of Person then it will print the name

Class Test
 {
  public static void main(String... args){
    Person obj = new Person("YourName");
    System.out.println(obj.toString());
  }
}

@Rohith K 2015-04-15 13:31:36

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

ReflectionToStringBuilder.toString(object)

@lukas84 2018-03-23 17:16:38

This has the advantage that it doesn't require to edit the class, which is sometimes not possible. However, how can I recursively print nested objects too?

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