Compare Two Objects in Java with Possible Null Values

Compare two objects in Java with possible null values

This is what Java internal code uses (on other compare methods):

public static boolean compare(String str1, String str2) {
    return (str1 == null ? str2 == null : str1.equals(str2));
}

Comparing two objects, either of which could be null

There is new utility class available in jdk since 1.7 that is Objects .

This class consists of static utility methods for operating on
objects. These utilities include null-safe or null-tolerant methods
for computing the hash code of an object, returning a string for an
object, and comparing two objects.

You can use Objects.equals, it handles null.

Objects.equals(Object a, Object b) Returns true if the arguments are equal to each other and false
otherwise. Consequently, if both arguments are null, true is returned
and if exactly one argument is null, false is returned. Otherwise,
equality is determined by using the equals method of the first
argument.

if(Objects.equals(myString,myString2)){...}

How to compare two Strings when both can be null?

If Java 7+, use Objects.equals(); its documentation explicitly specifies that:

[...] if both arguments are null, true is returned and if exactly one argument is null, false is returned. Otherwise, equality is determined by using the equals method of the first argument.

which is what you want.

If you don't, your method can be rewritten to:

return s1 == null ? s2 == null : s1.equals(s2);

This works because the .equals() contract guarantees that for any object o, o.equals(null) is always false.

compare an object to null!

Try c != null in your if statement. You're not comparing the objects themselves, you're comparing their references.

Compare two objects with a check for null

Java 7.0 added a new handy class: Objects.

It has a method exactly for this: Objects.equals(Object a, Object b)

Compare 2 objects ignoring null values

I finally created my own asserts like this:

import org.assertj.core.api.AbstractAssert;
import org.assertj.core.api.Assertions;

import java.util.List;
import java.util.stream.Collectors;

public class Object1Assert extends AbstractAssert<Object1Assert, Object1> {

    public Object1Assert isEqualTo(Object1 other) {

        // specially for null
        if(actual == other) {return this;}

        if(actual.getObject2() != null) {
            Assertions.assertThat(other.getObject2()).isEqualToIgnoringNullFields(actual.getObject2());
        }

        if(actual.getObject3() != null) {
            for(Object3 object3 : actual.getObject3()) {
                my.package.Assertions.assertThat(object3).isIn(other.getObject3());
            }
        }
        // return the current assertion for method chaining
        return this;
    }

    public Object1Assert(Object1 actual) {
        super(actual, Object1Assert.class);
    }

    public static Object1Assert assertThat(Object1 actual) {
        return new Object1Assert(actual);
    }

}

public class Assertions {

    public static Object3Assert assertThat(Object3 actual) {
        return new Object3Assert(actual);
    }
}

public class Object3Assert extends AbstractAssert<Object3Assert, Object3> {

    public Object3Assert isIn(List<Object3> others) {
        List<String> otherStringIds = others.stream().map(Object3::getStringId).collect(Collectors.toList());
        Assertions.assertThat(otherStringIds).isNotEmpty();
        Assertions.assertThat(actual.getStringId()).isIn(otherStringIds);
        for (Object3 otherObject3 : others) {
            if(actual.getStringId().equalsIgnoreCase(otherObject3.getStringId())) {
                Assertions.assertThat(otherObject3).usingComparatorForType(Comparators.bigDecimalComparator, BigDecimal.class).isEqualToIgnoringNullFields(actual);
            }
        }
        // return the current assertion for method chaining
        return this;
    }

    public Object3Assert(Object3 actual) {
        super(actual, Object3Assert.class);
    }

    public static Object3Assert assertThat(Object3 actual) {
        return new Object3Assert(actual);
    }

}

I created this class for each type I needed with this tutorial
https://www.baeldung.com/assertj-custom-assertion

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