why they are no need to import?

[Supun Lakshan Dissanayake]

To use classes in java packages we do import the whole package or necessary classes.
But we NEVER import some classes like String, Integer, Double, Object.
How can we use them without import them?

[Darryl Burke]

Read about it in The Java™ Language Specification.

Every compilation unit implicitly imports every public type name declared in the predefined package java.lang, as if the declaration import java.lang.*; appeared at the beginning of each compilation unit immediately after any package statement. As a result, the names of all those types are available as simple names in every compilation unit.

[vinay chaturvedi]

The java classes such as String, Number, StringBuffer, StringBuilder, Object, etc. are present in package "java.lang". In every java class this java.lang package is by default imported.
Hence all these classes are available in a class.

[Supun Lakshan Dissanayake]

Thanks Guys!! problem resolved.