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

java

reflection

tostring

debugging

byNikita Barsukov·Oct 21, 2024

To customize the output of your Java object, override the toString() method in your class like so:

public class MyObject {
    private int id;
    private String name;

    // Constructor... Ain't he a good guy?
    public MyObject(int id, String name) {
        this.id = id;
        this.name = name;
    }

    // Custom toString() implementation, 'cause we don't like generic stuff, right?
    @Override
    public String toString() {
        return String.format("MyObject{id=%d, name='%s'}", id, name);
    }
}

// Usage
MyObject obj = new MyObject(1, "JavaBean");
System.out.println(obj); // Prints: MyObject{id=1, name='JavaBean'}

Advanced strategies with toString()

Libraries to the rescue

Ever heard of ReflectionToStringBuilder from Apache Commons Lang library? It's a detailed string representation of the object's state, ideal for debugging and logging:

import org.apache.commons.lang3.builder.ReflectionToStringBuilder;

// Using ReflectionToStringBuilder, or as I like to call it, the "tell me what you got" builder
System.out.println(ReflectionToStringBuilder.toString(obj));

When dealing with array objects, Arrays.toString() and Arrays.deepToString() are life-savers. It's like a toString() for arrays without the fuss!

import java.util.Arrays;

int[] array = {1, 2, 3};
// Array's first day at school picture - a single-dimensional array
System.out.println(Arrays.toString(array));  // [1, 2, 3]

int[][] matrix = {{1, 2}, {3, 4}};
// Now we're getting deep, it's inception time with a multi-dimensional array 
System.out.println(Arrays.deepToString(matrix));  // [[1, 2], [3, 4]]

Wise use of IDEs

Modern IDEs such as IntelliJ IDEA and Eclipse have automated toString() generation. It's like having a personal assistant to write boring toString() methods.

JSON beauty with Gson

For converting Java objects to JSON strings, Gson's pretty printing makes it look like poetry:

import com.google.gson.GsonBuilder;

// Gson, turning your plain old Java object into a beautiful JSON-string supermodel
String json = new GsonBuilder().setPrettyPrinting().create().toJson(obj);
System.out.println(json);

Ultimate toString tips

Performance boost with StringBuilder

For large objects or in heavy loops, a StringBuilder in your toString() is like putting a Tesla engine in your car:

@Override
public String toString() {
    // And they said Rome wasn't built in a day...
    StringBuilder sb = new StringBuilder("MyObject{");
    sb.append("id=").append(id);
    sb.append(", name='").append(name).append('\'');
    sb.append('}');
    return sb.toString();
}

Handling nulls

Prevent NullPointerException by treating potential null values like polite guests:

public String toString() {
    // Handle null name like a secret agent undercover as "Nameless"
    return String.format("MyObject{id=%d, name='%s'}", id, Objects.toString(name, "Nameless"));
}

Collections and toString()

In classes like List, Set, or Map, ensure that each element's toString() is like an Oscar-winning actor, so your collection is nothing less than a star-studded movie.

Tricky situations and how to handle them

Circular references: Prioritize your sanity over endless loops. Break circular dependencies in toString().
Sensitive data: Passwords in toString()? Nope. Exclude sensitive fields or use text replacement techniques.
Performance: Cache your toString() result if it's called repeatedly and tends to stay the same. It's like saving your favorite pizza place as a speed dial.