Wrapper Methods

The wrapper classes provide three important methods for converting data:

• static type parseType(String)
• static Type valueOf(type)
• type typeValue()

static type parseType(String)

Attempt to convert a String to a value of the wrapper class's corresponding primitive type.

• Character is the only wrapper without this method.

• parseType is a static method, usually called in a static manner:

int countArg = 0;
if ( args.length > 0 ) {
  countArg = Integer.parseInt(args[0]);
}

• If the string can't be parsed to the given type, a NumberFormatException will be thrown.

Drill

WrapperClasses/com.example.wrapperclasses.drills.ParseDrill * Use println statements to test the parseability and results for each string.

static Type valueOf(type)

Convert the passed primitive type (or String) to a wrapper-class object.

Integer iObject = Integer.valueOf(500);
Double dObject = Double.valueOf(2.718);
Boolean bObject = Boolean.valueOf(false);

* Except for Character all the wrappers have a String version of valueOf, which behaves like parseType but returns a wrapper-class object instead of a primitive.

Byte byteObject = Byte.valueOf("-128");
Long longObject = Long.valueOf("2147483648");

Note that these methods take a parameter of the corresponding primitive type.

Short shortObject = Short.valueOf(123);

will not compile, because 123 is an int literal; you must cast it to short to match the signature of .Short.valueOf().

Short shortObject = Short.valueOf((short)123);

type typeValue()

Return the primitive-type value encapsulated by this wrapper object.

byte b = byteObject.byteValue();
double d = dObject.doubleValue();
boolean bool = bObject.booleanValue();

• The wrappers that extend Number each have the following methods for yielding their value as a different data type:

• byteValue

• doubleValue
• floatValue
• intValue
• longValue
• shortValue

toString

As with all objects, each wrapper object has a toString.

In addition, the wrapper classes have a static toString that takes the primitive type as an argument.

System.out.println(Double.toString(2414e-3)); // 2.414

The numeric wrappers have variants for converting a number to a string representing binary, octal, etc.

System.out.println(Integer.toBinaryString(32766)); // 111111111111110
System.out.println(Integer.toHexString(32766));    // 7ffe

Practice Exercise

Wrapper Constructors

While the wrapper classes have constructors, these are deprecated starting in Java version 9. Instead, always use the appropriate valueOf() method to convert a primitive type to a wrapper object, and the appropriate parseValue() method to convert a String to a wrapper.

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