Multi tool use

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

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.

com.foo.Person@2f92e0f4

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

Person

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


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

[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.}

9 Answers
9

Background

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

toString()

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:

Object

Object.toString()

@

// 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@2f92e0f4

com.foo.MyType

MyType

com.foo

@

2f92e0f4

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:

Class.getName()

[Ljava.lang.String

[

[[

[[[

L

java.lang.String

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:

System.out.println(myObject)

toString()

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.

Person

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:

toString()

toString()

Person

@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.

Person[name=Henry]

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() {...}.

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.

toString()

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

ToStringBuilder from Apache Commons Lang

ToStringBuilder

MoreObjects.ToStringHelper from Google Guava

MoreObjects.ToStringHelper

@ToString annotation from Project Lombok

@ToString

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?

toString()

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:

Arrays.toString()

Person

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.

toString()

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

Arrays.deepToString()

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

.toString()

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.

toString()

return String.format( getClass().getSimpleName() + "[ name=%s ]", name);

name

getName()

return String.format( getClass().getSimpleName() + "[ name=%s ]", getName());

Arrays.toString()

int

double

Arrays.deepToString()

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

ReflectionToStringBuilder.toString(object)


Every class in java has toString() method in it by default, which is called by System.out.println() if you pass some object of a class to it. When you try to print object of a class, the System.out.println() method will call toString() of the class which returns the className@hashcode of that object.

toString()

System.out.println()

System.out.println()

toString()

{
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);
}
}


[Lcom.foo.Person;@28a418fc

toString()

Person

Person

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

toString()

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

toString()

If you Directly print any object of Person It will the ClassName@HashCode to the Code.

ClassName@HashCode

in your case com.foo.Person@2f92e0f4 is getting printed . Where Person is a class to which object belongs and 2f92e0f4 is hashCode of the Object.

com.foo.Person@2f92e0f4

Person

2f92e0f4

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

Person

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


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).

By default, every Object in Java has the toString() method which outputs the ObjectType@HashCode.

toString()

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

toString()

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.

System.out.prtinln(personObj);

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.

[Lcom.foo.Person;@28a418fc

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. :)

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.

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]];


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