Eclipse Problems View Not Showing Errors Anymore

Eclipse problems view not showing warnings

This could be a problem with the Java compiler settings where you describe whether each kind compile issue (e.g. local value not read, etc.) is to be treated as an error, warning or simple ignored.

Go to Preferences -> Java -> Compiler -> Errors/Warnings and confirm that the warnings you expect to be flagged are in fact configured to be warnings.

Eclipse Problems View doesn't show Errors

For anyone else who is having this problem, I have found the answer:

Make sure that Eclipse recognizes your project as a Java project. Specifically, under Project Properties ensure that you have a Java Builder that is checked.

That way, your project will be built and you will see errors in the Problems view.

Eclipse is not showing compilation errors in project explorer

As I can see in your project explorer there is a RED exclamation mark over your project name which means there is a problem with the build path in your project. See here for more details.

Check the Build Path of the project by right-clicking the project and selecting Build Path -> Configure Build Path.
One problem I often encountered is different people using different Java SDK and so when the exact SDK is not available on your machine, you need to change to your Java SDK (via JRE System Library -> Alternate JRE). A better way to avoid this problem is to always select the JRE System Library from Workspace default JRE or Execution Environment.

Eclipse console not showing standard errors

So I went ahead and reinstalled Eclipse, I don't know why but it appears to be working now.

Eclipse editor not showing error markers

Check the Build Path of the project by right clicking the project and select Build Path -> Configure Build Path.

JDK is not properly configure for project. Configure your JDK instead of in-build JRE.

Also make sure your source folder is also configure in Build Path (for example MyProject/src) must listed as a Source folder.

In Java Compiler-->Errors/warning, click Restore Default.

Make sure "Build Automatically" is checked.

Eclipse won't check for errors in my code (Java EE)

Check if the project has any problems in the "problems" fast view. Sometimes, Eclipse refuses to build automatically if there is a problem such as a cyclic module dependency, or some required .class file being referenced indirectly.

Here are some links:

Eclipse Problems View not showing Errors anymore
Best Practices for Eclipse's Problems View
http://help.eclipse.org/help32/index.jsp?topic=/org.eclipse.platform.doc.user/concepts/cprbview.htm