01
Capture the complete missing signature
Record the declaring class, method name, parameters, and return type shown by the error. A class existing under the expected name does not mean that its binary provides the method the caller expects.
Our older library exposed Greeting.message(), while the newer one exposed Greeting.message(String). The application compiled against the latter. Launching it with the former produced NoSuchMethodError at the method call instead of a missing-class error.
02
Create the intentionally older API
Save this local fixture as v1/demo/api/Greeting.java. It exposes only the no-argument message method. It is compiled into its own JAR so the runtime can deliberately select it without changing any application installation.
This is synthetic test code, not a version recommendation for a real library. The purpose is to make the binary signature difference independently inspectable.
package demo.api;
public class Greeting {
public static String message() { return "hello"; }
}03
Create the API expected by the caller
Save the second fixture as v2/demo/api/Greeting.java. It has the same binary class name but a different method signature: the caller supplies a String. Keep its output directory separate from v1.
Compile the application against this second definition, then select v1 only in the failing runtime launch. That reproduces a mismatch between the compiled caller and the binary that the JVM actually loads.
package demo.api;
public class Greeting {
public static String message(String name) { return "hello " + name; }
}04
Use a small caller to isolate binary compatibility
The following caller assumes demo.api.Greeting has a static message method accepting String. Save it as MethodApp.java. Keep two versions of a test library in separate build directories; do not overwrite a production dependency to reproduce the problem.
For the local experiment, the compatible library’s method returned hello followed by the supplied name. The older version had only a no-argument overload. Those signatures are distinct to the JVM.
import demo.api.Greeting;
public class MethodApp {
public static void main(String[] args) {
System.out.println(Greeting.message("developer"));
}
}05
Inspect the runtime class source and methods
Use class-load logging during an authorized reproduction to identify the JAR that supplies the class. Then inspect that specific artifact with javap. Inspecting the copy in a build cache does not prove that the running process loaded it.
The commands below assume out/app contains the compiled caller and v1.jar is the intentionally incompatible library. The first call fails as designed. Our logs identified demo.api.Greeting from v1.jar, and javap showed only message().
mkdir -p out/v1 out/v2 out/app
javac -d out/v1 v1/demo/api/Greeting.java
javac -d out/v2 v2/demo/api/Greeting.java
jar --create --file v1.jar -C out/v1 .
jar --create --file v2.jar -C out/v2 .
javac -cp v2.jar -d out/app MethodApp.java
# Expected failure with the deliberately incompatible test library:
java -Xlog:class+load=info -cp 'out/app:v1.jar' MethodApp
javap -classpath v1.jar demo.api.Greeting06
Align the runtime dependency deliberately
Resolve why an older or otherwise incompatible JAR is selected. Check the distribution, container layers, launch script, dependency mediation, and any platform-provided libraries. Changing classpath order without understanding duplicates can leave another call path broken.
In the controlled test, running the same compiled caller with v2.jar produced hello developer. In a real application, rebuild the distribution with an intentional supported dependency set and verify that the expected binary is loaded.
# Same caller, compatible test dependency:
java -cp 'out/app:v2.jar' MethodApp07
Exercise affected callers after the change
A dependency change can fix one caller while breaking another caller compiled against different expectations. Test representative application paths through the packaged artifact rather than relying on a single successful method invocation.
Keep the error signature, loaded-class origin, selected dependency version, and verification result together. That evidence separates binary incompatibility from an assumed JVM-version problem and makes future dependency drift easier to detect.
Know the limits
Reproduced with Eclipse Temurin OpenJDK 25.0.4.1+1 in a disposable Linux container with no external network. The app compiled against a method accepting String, then loaded an older JAR exposing only a no-argument method. Class-load logging identified that JAR; aligning the runtime version fixed the call. Maven/Gradle mediation and framework class loaders were not exercised.
Sources & further reading
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