Last Time

• We learned what String[] args is: it is an array of strings that holds command-line arguments entered by the executor of the program.
• We learned that static items are properties of the class as a whole. Items that arae not static are called instance items.
• The rule of the greased wall says that instance items have access to static items, but static items do not have naked access to instance items.
• Java has static service classes such as Math and Arrays which are just containers that hold useful static methods.
• Every primitive type has a corresponding wrapper type that is an object. Wrapper classes include useful static methods that do useful stuff with the primitive they wrap.
• You can assign directly to wrapper types. This code is legit.

  
  Integer x = 4;   //autoboxing
  int z = x;       //autounboxing
  

Other Wrapper Types

We will explore the rest of the wrapper types using jshell. Here is a decoder ring.

Here are common featurs to all wrapper classes.

• All of these create immutable objects.
• All have a static toString method.
• All reside in package java.lang so no import statement is necessary.
• All numeric types have static MAX and MIN static constants.
• All numeric types have static SIZE and BYTES static constants.
• All have a parse method to cast a string to the primitive type.

Here is a use case for one of the parse methods.

import java.util.Scanner;
public class Hoover
{
    public static void main(String[] args)
    {
        Scanner vacuum = new Scanner(System.in);
        System.out.print("Enter a integer:  ");
        String foo = vacuum.next();
        int x = Integer.parseInt(foo);
        System.out.printf("The square of %s is %s.\n", x, x*x);
    }
}