Is there a Java utility to do a deep comparison of two objects?

user_23072 0
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How to "deep"-compare two objects that do not implement the equals method based on their field values in a test?

Original Question (closed because lack of precision and thus not fulfilling SO standards), kept for documentation purposes:

I'm trying to write unit tests for a variety of clone() operations inside a large project and I'm wondering if there is an existing class somewhere that is capable of taking two objects of the same type, doing a deep comparison, and saying if they're identical or not?

equals comparison java
15 Answers

In AssertJ, you can do:

Assertions.assertThat(expectedObject).isEqualToComparingFieldByFieldRecursively(actualObject);

Probably it won't work in all cases, however it will work in more cases that you'd think.

Here's what the documentation says:

Assert that the object under test (actual) is equal to the given object based on recursive a property/field by property/field comparison (including inherited ones). This can be useful if actual's equals implementation does not suit you. The recursive property/field comparison is not applied on fields having a custom equals implementation, i.e. the overridden equals method will be used instead of a field by field comparison.

The recursive comparison handles cycles. By default floats are compared with a precision of 1.0E-6 and doubles with 1.0E-15.

You can specify a custom comparator per (nested) fields or type with respectively usingComparatorForFields(Comparator, String...) and usingComparatorForType(Comparator, Class).

The objects to compare can be of different types but must have the same properties/fields. For example if actual object has a name String field, it is expected the other object to also have one. If an object has a field and a property with the same name, the property value will be used over the field.

user_18555790

Apache gives you something, convert both objects to string and compare strings, but you have to Override toString()

obj1.toString().equals(obj2.toString())

Override toString()

If all fields are primitive types :

import org.apache.commons.lang3.builder.ReflectionToStringBuilder;
@Override
public String toString() {return 
ReflectionToStringBuilder.toString(this);}

If you have non primitive fields and/or collection and/or map :

// Within class
import org.apache.commons.lang3.builder.ReflectionToStringBuilder;
@Override
public String toString() {return 
ReflectionToStringBuilder.toString(this,new 
MultipleRecursiveToStringStyle());}

// New class extended from Apache ToStringStyle
import org.apache.commons.lang3.builder.ReflectionToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;
import java.util.*;

public class MultipleRecursiveToStringStyle extends ToStringStyle {
private static final int    INFINITE_DEPTH  = -1;

private int                 maxDepth;

private int                 depth;

public MultipleRecursiveToStringStyle() {
    this(INFINITE_DEPTH);
}

public MultipleRecursiveToStringStyle(int maxDepth) {
    setUseShortClassName(true);
    setUseIdentityHashCode(false);

    this.maxDepth = maxDepth;
}

@Override
protected void appendDetail(StringBuffer buffer, String fieldName, Object value) {
    if (value.getClass().getName().startsWith("java.lang.")
            || (maxDepth != INFINITE_DEPTH && depth >= maxDepth)) {
        buffer.append(value);
    } else {
        depth++;
        buffer.append(ReflectionToStringBuilder.toString(value, this));
        depth--;
    }
}

@Override
protected void appendDetail(StringBuffer buffer, String fieldName, 
Collection<?> coll) {
    for(Object value: coll){
        if (value.getClass().getName().startsWith("java.lang.")
                || (maxDepth != INFINITE_DEPTH && depth >= maxDepth)) {
            buffer.append(value);
        } else {
            depth++;
            buffer.append(ReflectionToStringBuilder.toString(value, this));
            depth--;
        }
    }
}

@Override
protected void appendDetail(StringBuffer buffer, String fieldName, Map<?, ?> map) {
    for(Map.Entry<?,?> kvEntry: map.entrySet()){
        Object value = kvEntry.getKey();
        if (value.getClass().getName().startsWith("java.lang.")
                || (maxDepth != INFINITE_DEPTH && depth >= maxDepth)) {
            buffer.append(value);
        } else {
            depth++;
            buffer.append(ReflectionToStringBuilder.toString(value, this));
            depth--;
        }
        value = kvEntry.getValue();
        if (value.getClass().getName().startsWith("java.lang.")
                || (maxDepth != INFINITE_DEPTH && depth >= maxDepth)) {
            buffer.append(value);
        } else {
            depth++;
            buffer.append(ReflectionToStringBuilder.toString(value, this));
            depth--;
        }
    }
}}
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