• Develop code to use Integer and Double objects from their primitive counterparts and determine the result of using these objects

Assignment

Believe it or not, objects are sometime preferable to primitives. That means having a plain int is a detriment in some cases, where an object would be more desirable, if not necessary.

One quick reason why (as others won’t make sense at the moment) is that the absence of data is best represented by null, which primitives can’t ever be.

Enter wrapper classes, which take primitives and wrap them in objects. While there is a wrapper class for each primitive, you only need to worry about Integer and Double. Working with them is straightforward since Java will do something called autoboxing and unboxing, meaning it automatically converts one to the other.

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Integer i = 5;  // autoboxing
int j = i;      // unboxing

You can still use the new keyword if you wish, but there’s no need (and it’s actually depreciated as of a Java 9 almost 10 years ago).

Also, wrapper classes are part of a java.lang so they are loaded by default and don’t require an import statement.

Parsing Methods

Like any other class, wrappers come with methods, but the only two you need to worry about are

  • static int parseInt(String s)
  • static double parseDouble(String s)

Both will convert a string to the appropriate number, provided the string can actually be converted. Note they are static, so remember to put the class name in front.

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String str = "53";
int i = Integer.parseInt(str);

Remember MAX_VALUE and MIN_VALUE?

Of course you do. Go look at 1.5 Casting and Ranges of Values for a refresher. Both of those are fields in the Integer class.