Check String is Isomorphic

Two strings are isomorphic if the characters in string1 can be mapped by the exact same character in string2. 2 different characters should not be mapped to the same character but a character may map to itself. the order of the characters should be& preserved.

For example in the string EGG and ADD

Both string EGG and ADD are isomorphic since each character of String 1 has unique mapping with the character of String 2

In string wesome.org and wesome.org

both strings are isomorphic since each character is mapped to itself.

package org.wesome.dsalgo;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

public class Isomorphic {
    public static boolean isIsomorphic(String str1, String str2) {
        // Two strings cannot be isomorphic if they have different lengths.
        if (str1.length() != str2.length()) {
            return false;
        }
        // map will store mappings of str1 chars to str2 chars.
        Map<Character, Character> map = new HashMap<>();
        // set to keep track of already mapped characters.
        Set<Character> set = new HashSet<>();
        for (int i = 0; i < str1.length(); i++) {
            char char1 = str1.charAt(i);
            char char2 = str2.charAt(i);
            // If char1 has been encountered before:
            if (map.containsKey(char1)) {
                // Return false if first occurrence of char1 is mapped to a different character.
                if (map.get(char1) != char2) {
                    return false;
                }
            }
            // If char1 is encountered for the first time, it has not been mapped yet:
            else {
                // Return false if char2 is already mapped to some other char in str1
                if (set.contains(char2)) {
                    return false;
                }
                // insert in the map, and the set.
                map.put(char1, char2);
                set.add(char2);
            }
        }
        return true;
    }
}

package org.wesome.dsalgo;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

public class IsomorphicTest {
    @Test
    void IsomorphicTest1() {
        String string1 = "egg", string2 = "add";
        Assertions.assertTrue(Isomorphic.isIsomorphic(string1, string2));
    }

    @Test
    void IsomorphicTest2() {
        String string1 = "paper", string2 = "title";
        Assertions.assertTrue(Isomorphic.isIsomorphic(string1, string2));
    }

    @Test
    void IsomorphicTest3() {
        String string1 = "wesome.org", string2 = "wesome.org";
        Assertions.assertTrue(Isomorphic.isIsomorphic(string1, string2));
    }
}

plugins {
    id 'java'
}

group = 'org.wesome'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = JavaVersion.VERSION_1_8

configurations {
    compileOnly {
        extendsFrom annotationProcessor
    }
}

repositories {
    mavenCentral()
}

dependencies {
    testImplementation 'org.junit.jupiter:junit-jupiter:5.6.2'
}

test {
    useJUnitPlatform()
}