Simple Java implementation of some patterns I really enjoy from Kotlin.

JavaUtil.java

class JavaUtil {
    /**
     * Runtime checks, similar to the Kotlin standard library check method.
     */
    public static void check(boolean condition, String message) {
        if (!condition) {
            throw new IllegalStateException(message);
        }
    }

    public static void check(boolean condition) {
        check(condition, "check failed");
    }

    /**
     * Silence annoying IDE errors when drafting methods, similar to the Kotlin
     * standard library method.
     * For method stubs, simply `return TODO("Not implemented");`.
     */
    @SuppressWarnings("UnusedReturnValue")
    public static <T> T TODO(String message) {
        throw new IllegalStateException(message);
    }

    public static <T> T TODO() {
        throw new IllegalStateException("TODO");
    } 
}