🚀 JPlus

A Java superset language running on the JVM,
JPlus is a modern programming language that significantly boosts developer productivity while fully leveraging the existing Java ecosystem.

✨ Project Overview

JPlus is fully compatible with Java, offering modern language features like null safety, type inference, and functional programming to reduce developer burden and maximize productivity.

Notably, there is currently no ‘superset’ language that keeps Java syntax almost intact while extending the language with features like null checks at the language level. JPlus aims to fill this gap, providing a language that existing Java developers can naturally learn and adopt.

Why JPlus?

Maintains Java Compatibility
Fully utilizes existing Java libraries and frameworks
Enhances Development Productivity
Automates null checks, supports boilerplate code generating syntax and other modern features
Allows Gradual Adoption
Existing Java code can remain unchanged while selectively adopting JPlus syntax
Compiles to Plain Java Code
Converts JPlus syntax into clean, version-flexible Java code that runs on any standard Java compiler or JVM without extra dependencies.

🛠️ Key Features

Feature	Description
Strict Null Checking	Prevents null reference errors at compile time
Boilerplate Code Genererating	Minimizes boilerplate code
Asynchronous Syntax	Simple async/await-style asynchronous handling
Concise Syntax	smart casts and more for clearer and shorter code

🚀 IntelliJ Plugin 0.1 MVP Alpha Release!

We’re excited to announce the release of JPlus IntelliJ Plugin (v0.1-mvp-alpha)! 🎉

📥 Download: intellij-plugin-0.1-mvp-alpha.zip

✨ Key Features

Write JPlus code directly in IntelliJ IDEA
Full IDE Support: syntax highlighting, code completion, and error checking
Nullability Checker: ensures safe handling of null values at compile-time
Seamless Java Integration: easily use JPlus alongside your existing Java projects

🎥 Watch the demo video: JPlus IntelliJ Plugin Demo

Your early feedback will be invaluable in helping us polish the plugin before the official launch. Stay tuned – the public release is coming soon!

🚀 New Feature: Apply Syntax for Boilerplate Elimination

JPlus introduces a powerful new apply syntax to replace common boilerplate patterns previously handled by Lombok annotations. This declarative syntax helps you reduce repetitive code like getters, setters, constructors, equals/hashCode, and builders — all in a clean, compact form.

🔍 Overview

JPlus `apply` Syntax	Equivalent Lombok Annotation
`data`	`@Data`
`getter`	`@Getter`
`setter`	`@Setter`
`equals`, `hashCode` or combined `equality`	`@EqualsAndHashCode`
`toString`	`@ToString`
`constructors(no)`	`@NoArgsConstructor`
`constructors(all)`	`@AllArgsConstructor`
`constructors(required)`	`@RequiredArgsConstructor`
`builder`	`@Builder`
`value` or `immutable`	`@Value`
`logger(slf4j)` / `logger(java)`	`@Slf4j` / `@Log`

Additional method-level and delegation features are also supported.

📝 Example Usage

apply data, builder, constructors(all, no);

apply {
    User.Profile: getter, setter, equality, constructor(all);
}

public class User {
    private String name;
    private int age;

    public class Profile {
        String nickname;
    }
}

For detailed example content, please refer to the following link.
Go to Example 6

🚧 Project Status: MVP

Please note that JPlus is currently in its MVP (Minimum Viable Product) stage.
This means the language is still under active development, features may be incomplete or subject to change, and bugs may exist.

We welcome feedback, bug reports, and contributions from the community to help shape and improve JPlus into a stable and powerful language.

💸 Support me on Github

💸 Support me on PayPal

⚙️ Installation & Execution

Follow these steps to get started with JPlus and run example programs.

1. Prerequisites

Java Development Kit (JDK) 17 or higher
```
java -version
```
Gradle installed (optional if using the provided Gradle wrapper)
```
gradle -v
```

2. Download JPlus Compiler

Currently, the JPlus compiler is distributed as a Gradle project. Clone the repository or download the latest release:

git clone https://github.com/nieuwmijnleven/JPlus.git
cd JPlus

3. Build the Project

Use the Gradle wrapper to build the compiler and run examples:

./gradlew app:build

4. Running Examples

To run a specific example file (e.g., NullableType1.jplus), use:

./gradlew run -Pargs="./src/test/samples/NullableType1.jplus"

Replace the argument path with any example you want to execute.

✅ Example ① - Compile-time null assignment check

JPlus explicitly defines nullability at the type system level and performs compile-time checks
to eliminate the possibility of NullPointerException at runtime.

📌 Basic Rules

Type → non-nullable (cannot be assigned null)
Type? → nullable (can be assigned null)
?. → safely access methods or fields on nullable objects

📄 Example – `NullableType1.jplus`

package jplus.example;

public class Main {
    public static void main(String[] args) {
        String? s1 = null;
        String s2 = null;
    }
}

s1 is a nullable variable and can be assigned null.
s2 is a non-nullable variable, so assigning null causes a compile-time error.

▶️ Run Command

./gradlew run -Pargs="./src/test/samples/NullableType1.jplus"

❌ Output

Error: (line:6, column:8) s2 is a non-nullable variable. But null value is assigned to it.

By enforcing explicit type declarations and compile-time null checks,
JPlus helps prevent null-related bugs early in the development process.

This approach is similar to strict null checking found in languages like Kotlin and TypeScript,
but with the key benefit of being gradually adoptable while preserving Java syntax.

✅ Example ② — Enforcing the null-safe operator (`?.`)

In JPlus, you must use the ?. operator when accessing nullable variables.
If you try to access fields or methods on a potentially-null object without the null-safe operator, a compile-time error will occur.

📄 Example – `NullableType2.jplus`

public class Main {
    public static void main(String[] args) {
        String? s1 = null;
        String s2 = "jplus";

        s1.length();
        s2.length();
    }
}

s1 is nullable but tries to call a method without using the null-safe operator (?.)
→ Compile-time error
s2 is non-nullable, so method access is allowed without issue

▶️ Run Command

./gradlew run -Pargs="./src/test/samples/NullableType2.jplus"

❌ Output

Error: (line:8, column:8) s1 is a nullable variable. But it direct accesses to length(). You must consider to use null-safe operator(?.)

✅ Corrected Code (Works as Expected)

s1?.length(); // null-safe access
s2.length();  // regular access

As shown above, JPlus enforces safe access to nullable variables at the language level,
helping to eliminate null-related runtime errors before they happen.

✅ Example ③ — Elvis Operator (`?:`)

JPlus introduces the Elvis operator (?:),
which allows you to easily provide a default or fallback value when a nullable variable is null.

📄 Example – `ElvisOperator.jplus`

package jplus.example;

public class Main {
    public static void main(String[] args) {
        String? s1 = null;
        String s2 = s1 ?: "jplus";
        System.out.printf("s1 = %s\n", s1 ?: "null-value");
        System.out.printf("s2 = %s\n", s2);
    }
}

s1 is a nullable variable.
s1 ?: "jplus" assigns "jplus" if s1 is null.
When printing, s1 ?: "null-value" safely handles null values.

▶️ Run Command

./gradlew run -Pargs="./src/test/samples/ElvisOperator.jplus"

✅ Output (Java code generated by JPlus)

package jplus.example;

public class Main {
    public static void main(String[] args) {
        String s1 = null;
        String s2 = (((s1) != null) ? (s1) : "jplus");
        System.out.printf("s1 = %s\n", (((s1) != null) ? (s1) : "null-value"));
        System.out.printf("s2 = %s\n", s2);
    }
}

The Elvis operator expression x ?: y is translated to Java's ternary expression (x != null) ? x : y.

✅ Example ④ — Correct Usage of the Null-safe Operator (`?.`)

In JPlus, the use of the null-safe access operator (?.) is enforced for nullable variables.
This prevents null reference errors and allows safe method calls on potentially null values.

📄 Example – `NullsafeOperator.jplus`

public class Main {
    public static void main(String[] args) {
        String? s1 = null;
        String s2 = "jplus";
        System.out.printf("the length of s1 : %d\n", s1?.length());
        System.out.printf("the length of s2 : %d\n", s2.length());
    }
}

s1 is a nullable variable.
s1?.length() safely returns null if s1 is null.
s2 is non-nullable, so calling length() is valid without safety checks.

▶️ Run Command

./gradlew run -Pargs="./src/test/samples/NullsafeOperator.jplus"

✅ Output (Java code generated by JPlus)

package jplus.example;

public class Main {
    public static void main(String[] args) {
        String s1 = null;
        String s2 = "jplus";
        System.out.printf("the length of s1 : %d\n", (s1 != null) ? s1.length() : null);
        System.out.printf("the length of s2 : %d\n", s2.length());
    }
}

This example demonstrates how JPlus handles the null-safe operator for nullable variables
and clearly shows how to write code that adheres to JPlus's null safety rules.

✅ Example ⑤ — Combining `?.` and `?:` Operators

JPlus supports combining the null-safe access operator (?.) and the Elvis operator (?:)
to simplify complex null-handling logic into clean and concise expressions.

📄 Example – `NullsafeWithElvisOperator.jplus`

package jplus.example;

public class Main {
    public static void main(String[] args) {
        String? s1 = null;
        String s2 = s1 ?: "jplus";
        System.out.printf("the length of s1 : %d\n", s1?.length() ?: 0);
        System.out.printf("the length of s2 : %d\n", s2.length());
    }
}

s1 is a nullable variable.
s1 ?: "jplus" → assigns "jplus" if s1 is null.
s1?.length() ?: 0 → safely calls length() on s1, returns 0 if s1 is null.
By combining both operators, null handling becomes safe and concise.

▶️ Run Command

./gradlew run -Pargs="./src/test/samples/NullsafeWithElvisOperator.jplus"

✅ Output (Java code generated by JPlus)

package jplus.example;

public class Main {
    public static void main(String[] args) {
        String s1 = null;
        String s2 = (((s1) != null) ? (s1) : "jplus");
        System.out.printf(
                "the length of s1 : %d\n",
                (((((s1 != null) ? s1.length() : null)) != null)
                        ? (((s1 != null) ? s1.length() : null))
                        : 0));
        System.out.printf("the length of s2 : %d\n", s2.length());
    }
}

The expression s1?.length() ?: 0 is translated into a nested conditional check in Java:
((s1 != null) ? s1.length() : null) != null ? ... : 0, ensuring safe execution.

✅ Example ⑥ — Using apply for Data Class and Nested Class Boilerplate Elimination

JPlus introduces the apply keyword to replace common Java boilerplate code such as getters, setters, constructors, builders, and more. It serves as a language-level alternative to Lombok annotations, offering a clean and declarative syntax.

📄 Example – `ApplyStatement.jplus`

package com.example;

apply data, constructor(required, all, no), builder;
apply {
    User.Profile: getter, setter, equality, constructor(all);
}

public class User {
    private String name;
    private int age;

    public class Profile {
        String nickname;
    }
}

data: Automatically generates getters, setters, equals(), hashCode(), and toString()
builder: Generates a User.Builder class for fluent object creation
constructors(required, all, no):Generates a constructor with all/required fields and a no-argument constructor
equality: Generates equals() and hashCode() methods
apply { User.Profile: ... }: Applies boilerplate generation specifically to the Profile inner class

▶️ Run Command

./gradlew run -Pargs="./src/test/samples/ApplyStatement.jplus"

✅ Output (Java code generated by JPlus)

package com.example;

//apply data, constructor(required, all, no), builder;
//apply {
//    User.Profile: getter, setter, equality, constructor(all);
//}

public class User {
    private String name;
    private int age;

    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public User() {}

    public class Profile {
        String nickname;

        public Profile(String nickname) {
            this.nickname = nickname;
        }

        public String getNickname() {
            return nickname;
        }

        public void setNickname(String nickname) {
            this.nickname = nickname;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Profile profile = (Profile) o;
            return java.util.Objects.equals(nickname, profile.nickname);
        }

        @Override
        public int hashCode() {
            return java.util.Objects.hash(nickname);
        }
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" + "name=" + name+ ", " + "age=" + age + "}";
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        User user = (User) o;
        return age == user.age
                && java.util.Objects.equals(name, user.name);
    }

    @Override
    public int hashCode() {
        return java.util.Objects.hash(name, age);
    }

    public static class Builder {
        private String name;
        private int age;

        public Builder name(String name) {
            this.name = name;
            return this;
        }

        public Builder age(int age) {
            this.age = age;
            return this;
        }

        public User build() {
            return new User(name, age);
        }
    }

    public static Builder builder() {
        return new Builder();
    }
}

🎯 Benefits of This Approach

✅ Eliminates the need for manual method and constructor generation
✅ Clean, declarative syntax – no annotations or external dependencies
✅ Fine-grained control over nested types (e.g. inner classes)
✅ All features translate into standard Java code at compile time

📘 Tip: Use apply {} block for Nested Classes

The apply block allows you to target specific nested or inner classes with scoped boilerplate logic:

apply {
    Outer.Inner: getter, setter;
}

This allows developers to keep code DRY and expressive even with deeply nested structures.

📌 Summary

This example demonstrates a natural combination of the following features:

✅ Null-safe method call (s1?.length())
Ensures safe access to nullable variables without throwing NullPointerException.
✅ Default fallback value (?: 0)
Provides a default value when an expression evaluates to null, improving code safety and readability.
✅ Declarative boilerplate generation with apply
The apply statement allows you to automatically generate common methods like getters, setters, equals(), hashCode(), toString(), and constructors without relying on annotations or third-party libraries like Lombok.

JPlus allows even complex null-handling logic to be expressed safely and concisely with its extended syntax.

📚 Summary of Examples

Example File	Description
`NullableType1.jplus`	Error when assigning `null` to a non-nullable variable
`NullableType2.jplus`	Error when accessing a nullable variable without `?.`
`ElvisOperator.jplus`	Handling null defaults using the Elvis operator `?:`
`NullsafeOperator.jplus`	Safe method call using the null-safe operator `?.`
`NullsafeWithElvisOperator.jplus`	Combining `?.` and `?:` for safe and concise null handling
`ApplyStatement.jplus`	Using apply to generate boilerplate and builder logic cleanly

🌟 Reference Examples

Kotlin: The leading JVM Java superset language
Scala: Combines functional and object-oriented paradigms, powerful but complex
Groovy: Emphasizes dynamic typing and conciseness
Xtend: Provides Java compatibility with concise syntax

🎯 JPlus Differentiators

Maintains maximum similarity to Java’s standard syntax
No existing ‘superset’ language keeps Java syntax almost unchanged while extending language-level null checks; JPlus fills this role
Enforces strict null safety
Supports gradual and flexible syntax extensions
Offers a gentle learning curve for Java developers

🤝 Sponsorship & Support

JPlus is currently in its MVP stage, and your support can make a big difference in shaping its future.

Report bugs, suggest features, and contribute code — every contribution helps!
By sponsoring, you help accelerate development and gain early access to new features.
We are preparing exclusive perks for sponsors as a token of our gratitude.

If you want to support the project financially, please visit our sponsorship page:

Become a Sponsor via Github

Become a Sponsor via PayPal.me

Thank you for helping us build a better, safer, and more productive programming language!

📄 License

JPlus is licensed under the Apache License 2.0.

Name		Name	Last commit message	Last commit date
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.intellijPlatform		.intellijPlatform
app		app
gradle		gradle
intellij-plugin		intellij-plugin
.gitattributes		.gitattributes
.gitignore		.gitignore
FUNDING.yml		FUNDING.yml
LICENSE		LICENSE
README.md		README.md
gradle.properties		gradle.properties
gradlew		gradlew
gradlew.bat		gradlew.bat
settings.gradle		settings.gradle

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🚀 JPlus

✨ Project Overview

Why JPlus?

🛠️ Key Features

🚀 IntelliJ Plugin 0.1 MVP Alpha Release!

✨ Key Features

🚀 New Feature: Apply Syntax for Boilerplate Elimination

🔍 Overview

📝 Example Usage

🚧 Project Status: MVP

⚙️ Installation & Execution

1. Prerequisites

2. Download JPlus Compiler

3. Build the Project

4. Running Examples

✅ Example ① - Compile-time null assignment check

📌 Basic Rules

📄 Example – NullableType1.jplus

▶️ Run Command

❌ Output

✅ Example ② — Enforcing the null-safe operator (?.)

📄 Example – NullableType2.jplus

▶️ Run Command

❌ Output

✅ Corrected Code (Works as Expected)

✅ Example ③ — Elvis Operator (?:)

📄 Example – ElvisOperator.jplus

▶️ Run Command

✅ Output (Java code generated by JPlus)

✅ Example ④ — Correct Usage of the Null-safe Operator (?.)

📄 Example – NullsafeOperator.jplus

▶️ Run Command

✅ Output (Java code generated by JPlus)

✅ Example ⑤ — Combining ?. and ?: Operators

📄 Example – NullsafeWithElvisOperator.jplus

▶️ Run Command

✅ Output (Java code generated by JPlus)

✅ Example ⑥ — Using apply for Data Class and Nested Class Boilerplate Elimination

📄 Example – ApplyStatement.jplus

▶️ Run Command

✅ Output (Java code generated by JPlus)

🎯 Benefits of This Approach

📘 Tip: Use apply {} block for Nested Classes

📌 Summary

📚 Summary of Examples

🌟 Reference Examples

🎯 JPlus Differentiators

🤝 Sponsorship & Support

📄 License

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📄 Example – `NullableType1.jplus`

✅ Example ② — Enforcing the null-safe operator (`?.`)

📄 Example – `NullableType2.jplus`

✅ Example ③ — Elvis Operator (`?:`)

📄 Example – `ElvisOperator.jplus`

✅ Example ④ — Correct Usage of the Null-safe Operator (`?.`)

📄 Example – `NullsafeOperator.jplus`

✅ Example ⑤ — Combining `?.` and `?:` Operators

📄 Example – `NullsafeWithElvisOperator.jplus`

📄 Example – `ApplyStatement.jplus`

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