A Makefile to compile a Maven/Gradle-style project layout using a custom JDK (for use w/ IE, Valhalla)

example-output.txt

[user@MSI java-jdk20-valhalla]$ make run
Java source files: src/main/java/org/example/Database.java src/main/java/org/example/PageLocation.java
Java class files:  target/classes/org/example/Database.class  target/classes/org/example/PageLocation.class
/home/user/downloads/jdk-20-vahalla-20-75/bin/java --enable-preview -cp target/classes org.example.Database
Hello World!
Page Location: PageLocation[databaseId=1, pageId=2]

Makefile

# Makefile to compile and run Java sources manually
# because JDK 20 Valhalla support is not yet available in IntelliJ IDEA
JAVA_VERSION = 20
JAVAC = /home/user/downloads/jdk-20-vahalla-20-75/bin/javac
JAVA = /home/user/downloads/jdk-20-vahalla-20-75/bin/java

JAVA_COMPILE_OPTIONS = --enable-preview --release $(JAVA_VERSION)
JAVA_OPTIONS = --enable-preview

JAVA_MAIN_CLASS = org.example.Database
JAVA_SOURCES = $(wildcard src/main/java/**/**/*.java)
JAVA_CLASSES = $(patsubst src/main/java/%.java, target/classes/%.class, $(JAVA_SOURCES))

# Compile the Java source files
compile: $(JAVA_CLASSES)
	$(info Java source files: $(JAVA_SOURCES))
	$(info Java class files: $(JAVA_CLASSES))

# Run the Java main class
run: compile
	$(JAVA) $(JAVA_OPTIONS) -cp target/classes $(JAVA_MAIN_CLASS)

# Clean the target directory
clean:
	rm -rf target

# Compile the Java source files
target/classes/%.class: src/main/java/%.java
	$(JAVAC) $(JAVA_COMPILE_OPTIONS) -d target/classes $<

# Create the target directory
target/classes:
	mkdir -p target/classes

# Make the target directory a dependency of the Java class files
$(JAVA_CLASSES): target/classes

# Make the target directory a dependency of the compile target
compile: target/classes
# Ditto...
clean: target/classes
run: target/classes
default: target/classes

default: run

source-files.java

// ./src/main/java/org/example/Database.java
package org.example;
class Database {
    public static void main(String[] args) {
        var examplePageLocation = new PageLocation(1, 2);
        System.out.println("Hello World!");
        System.out.println("Page Location: " + examplePageLocation);
    }
}

// ./src/main/java/org/example/PageLocations.java
package org.example;
public value record PageLocation(int databaseId, int pageId) {}