To get bindings across multiple files you will have to create temporary files of those char[]
and work with (from the ASTParser docs):
public void setEnvironment(String[] classpathEntries, String[] sourcepathEntries, String[] encodings, boolean includeRunningVMBootclasspath)
Sets the environment to be used when no IJavaProject is available. [...]
and
public void createASTs(String[] sourceFilePaths, String[] encodings, String[] bindingKeys, FileASTRequestor requestor, IProgressMonitor monitor)
Creates ASTs for a batch of compilation units. When bindings are being resolved, processing a batch of compilation units is more efficient because much of the work involved in resolving bindings can be shared.
When bindings are being resolved, all compilation units are resolved using the same environment, which must be set beforehand with setEnvironment. [...]