Those names such as "[I" and "[java.lang.String" are the internal names of "int" and "String". Paragraph 4.3 of the Java Virtual Machine Specification explains how these names work. For example, "[" means it's an array and "I" means "int".
The classes for arrays are things that are built-in into the compiler. You will not find a Java source file or *.class file anywhere for those classes.