3.1 Wrappers & StringsHomepage  « Java5 Certification « 3.1 Wrappers & Strings

In our first lesson within this section we start by looking at code that uses the primitive wrapper classes and/or autoboxing and unboxing. We then look at the differences between the String, StringBuilder, and StringBuffer classes.

Lets take a look at the points outlined at the Oracle Website for this part of the certification.

  • Section 3: API Contents

    • Develop code that uses the primitive wrapper classes (such as Boolean, Character, Double, Integer, etc.), and/or autoboxing & unboxing. Discuss the differences between the String, StringBuilder, and StringBuffer classes.

The Wrapper Classesgo to top of page Top

The wrapper classes provided in Java allow us to wrap any of the primitive types in an object. The benefits of this are two-fold:

  1. Wrapped primitives can be used in object-centric activities such as collections or where we need to use an object.
  2. Wrapped primitives give us access to utility functions that we can use with primitives.

The following table lists the primitive types, their wrapper classes and the constructors available:

Primitive Type Description Wrapper Constructor Arguments Examples
boolean and char
booleantrue/false valuesBooleanboolean or StringBoolean b1 = new Boolean(true);
Boolean b2 = new Boolean("false");
charCharacterCharactercharCharacter c = new Character('a');
signed numeric integers
byte8-bit integerBytebyte or Stringbyte b = 24;
Byte b1 = new Byte(b);
Byte b2 = new Byte("24");
shortShort integerShortshort or Stringshort s = 48;
Short s1 = new Short(s);
Short s2 = new Short("48");
intIntegerIntegerint or StringInteger i1 = new Integer(64);
Integer i2 = new Integer("64");
longLong integerLonglong or StringLong l1 = new Long (128);
Long l2 = new Long ("128");
signed floating point
floatSingle-precision floatFloatdouble, float or Stringdouble d = 123.456;
Float f1 = new Float(d);
Float f2 = new Float(123.456f);
Float f3 = new Float("123.456f");
doubleDouble-precision floatDoubledouble or StringDouble d1 = new Double(456.789);
Double d2 = new Double("456.789");

Strings In Javago to top of page Top

Most computer languages use the standard 8-bit ASCII character set which has a range of 0 to 127 to represent characters of a string. Java uses the Unicode character set which has a range of 0 to 65,536 that can represent any character found in any human language. The ASCII character set is a subset of Unicode and as such ASCII character are still valid in Java. In Java strings are objects and like any other object it means we can create (instantiate) them. Another thing to note about strings in Java is that they are immutable, which means once you have assigned a value to a String object it can never be changed.

See String Immutability for more on this.

See String Creation & Efficiency for more information on how Java uses the string constant pool.

String, StringBuilder, StringBuffer Differencesgo to top of page Top

String immutability can improve efficiency, the downside is we can also have a lot of strings that get lost in the string constant pool, when we reassign or discard our reference variables.

Luckily for us Java comes with the predefined StringBuffer and StringBuilder classes which we can use to modify strings without the pros and cons of immutability. So when you are doing a lot of string manipulation these are the classes to use. The StringBuilder class was introduced in Java5 as an alternative to the older StringBuffer class. Both these classes have the same API apart from the StringBuffer class being thread safe and having synchronized methods. For most situations when manipulating strings, thread safety isn't an issue and so the StringBuilder class is the better option for efficiency.

See the StringBuilder class lesson for more information about the StringBuilder and StringBuffer classes.

Related Java5 Tutorials

Beginning Java5 - Primitive Variables
API Contents - The String class
API Contents - The StringBuilder class

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