Introduction

This error comes from the old Eclipse ADT toolchain, not from modern Android Studio builds. It means the Eclipse project was configured with a Java compiler level that the legacy Android tooling did not expect, so ADT asks you to repair the project settings.

Why the Error Appears

Older Android Eclipse projects were tightly coupled to specific Java source and bytecode levels. If Eclipse switched the project compiler compliance to 1.7, ADT could reject it and show this message because the project metadata and Android tooling no longer agreed.

Typical causes were:

• importing an old Android project into a newer Eclipse workspace
• changing the installed JDK or workspace defaults
• letting Eclipse update project compiler settings without updating Android project metadata

In that environment, the problem is not your Java code alone. It is the mismatch between ADT expectations and Eclipse project configuration.

Fix the Project in Eclipse

If you are truly working in the old Eclipse ADT stack, the usual repair steps are:

1. right-click the project
2. open Properties
3. go to Java Compiler
4. enable project-specific settings
5. set the compiler compliance level to 1.5 or 1.6

Then run the ADT repair command:

• 'Android Tools'
• 'Fix Project Properties'

Also verify the Java build path:

• open Java Build Path
• make sure the project is using the intended JRE/JDK
• remove conflicting libraries if Eclipse attached the wrong one

The ADT repair step updates metadata files that Eclipse alone may not correct.

Understand the Historical Context

This error is a sign you are in a legacy build environment. Modern Android development does not use the old ADT "Fix Project Properties" workflow. Android Studio and Gradle manage Java and Android build settings differently.

A modern Gradle configuration looks more like this:

1android {
2    compileOptions {
3        sourceCompatibility = JavaVersion.VERSION_17
4        targetCompatibility = JavaVersion.VERSION_17
5    }
6}

So if you see the exact "Fix Project Properties" message, you are almost certainly dealing with an older Eclipse-based project rather than a current Android Studio project.

When Migration Is the Better Fix

If the project still matters, migrating from Eclipse ADT to Android Studio is often a better long-term solution than continuing to repair old Eclipse metadata. The legacy toolchain is fragile, and these compatibility issues tend to keep returning whenever the workspace or Java installation changes.

Migration may take effort, but it removes an entire class of build-environment problems tied to obsolete Android tooling.

Common Pitfalls

The biggest mistake is trying to solve this as if it were a modern Gradle or Android Studio problem. It is not. The error message itself points to the older Eclipse ADT workflow.

Another common issue is changing the workspace JRE while forgetting that the project still has its own compiler settings and Android metadata. Both layers need to agree.

People also force a newer compiler level into a legacy ADT project and assume the build tools will adapt. They usually will not.

Finally, if the project is actively maintained, do not spend too much time polishing a dead toolchain. At some point, migration is the more practical engineering decision.

Summary

• This error belongs to the old Eclipse ADT Android toolchain.
• It usually means the Eclipse compiler level and Android project metadata no longer match.
• Set the project compiler compliance back to 1.5 or 1.6 in that legacy environment.
• Run Android Tools > Fix Project Properties to repair ADT metadata.
• For actively maintained apps, migrating to Android Studio is usually the better long-term fix.