The Solidity language is statically typed. When writing a contract or library definition, all of the state variables and local variables must have the data type specified along with its declaration. There are many data types supported by Solidity. You can create your own custom type by using the data types supported by Solidity; for example, you can define your complex struct variable.
Solidity also has a support for the var keyword, used for dynamic data type. However, since Solidity version 0.4.20, the var keyword has been deprecated because of security concerns.
If we look at the Java language, it has primitive data types and reference data types. For reference data types, especially for instantiable class, the default value is null while initialization. However, in Solidity, there is no concept of null values. Instead of null, the...