[java] 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.

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.}

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.

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);
    }
}

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.

I managed to get this done using Jackson in Spring 5. Depending on the object Jackson might not work in all cases.

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

ObjectMapper mapper = new ObjectMapper();
Staff staff = createStaff();
// pretty print
String json = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(staff);
System.out.println("-------------------------------------------------------------------")
System.out.println(json);
System.out.println("-------------------------------------------------------------------")

the output would be something like

-------------------------------------------------------------------
{
  "id" : 1,
  "internalStaffId" : "1",
  "staffCms" : 1,
  "createdAt" : "1",
  "updatedAt" : "1",
  "staffTypeChange" : null,
  "staffOccupationStatus" : null,
  "staffNote" : null
}
-------------------------------------------------------------------

More examples using Jackson here

You can try GSON also. Should be something like this:

Gson gson = new Gson();
System.out.println(gson.toJson(objectYouWantToPrint).toString());

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

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. :)

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);
    }
}

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).

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

ReflectionToStringBuilder.toString(object)

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

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.

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());
  }
}