Can we develop in Java without using the JDK?

No.

The JDK (Java Development Kit) includes the JRE (Java Runtime Environment) and a set of development tools such as the compiler (javac), debugger (jdb), and other utilities. Without the javac compiler, we cannot convert Java source code (.java files) into bytecode (.class files), which is then executed by the JVM (Java Virtual Machine) included in the JRE.

Of course, alternative JVMs and compilers that are not part of the official Oracle JDK can be considered (for example, OpenJDK, GraalVM), but the essence remains the same: for developing and compiling Java source code, a set of tools similar in functionality to the JDK is necessary.

Thus, for a complete Java development cycle (writing, compiling, packaging, running, debugging), it is impossible to do without some form of JDK.