Java efficient Programming (2)--Creating and destroying Objects

Item 1: Consider static factory methods instead of constructors

Advantage:

One advantage of static factory methods is, unlike constructors, they has names.

A second advantage of static factory methods is, unlike constructors, they was not required to create a new objec T each time they ' re invoked.

A third advantage of static factory methods is, unlike constructors, they can return an object of any subtype of Their return type.

A fourth advantage of static factory methods is that they reduce the verbosity (verbose) of creating parameterized Type Inst Ances.

Disadvantage:

The main disadvantage of providing only static factory methods are that classes without public or protected constructors cannot be subclassed.

A second disadvantage of static factory methods is, they is not readily distinguishable from other static methods .

Item 2: Consider a builder when faced with many constructor parameters

The telescoping constructor pattern works, but it was hard-to-write client code when there was many parameters, an D harder still to read it.

A JavaBean may is in the inconsistent state partway through its construction.

The JavaBeans pattern precludes the possibility of making a class immutable.

Advantage:

The Builder pattern simulates named optional parameters.

Class.newinstance breaks Compile-time exception checking.

The Builder pattern is a good choice when designing classes whose constructors or static factories would has more than a Handful of parameters.

Item 3:enforce the Singleton property with a private constructor or an enum type

Making A Class A singleton can make it difficult to test its clients.

A single-element enum type is the best implement a singleton.

#1. Singleton with public final field

 Public class Elvis {    publicstaticfinalnew  Elvis ();     Private Elvis () {...}      Public void leavethebuilding () {...}}

#2. Singleton with Static factory

 Public class Elvis {    privatestaticfinalnew  Elvis ();     Private Elvis () {...}      Public Static return INSTANCE;}      Public void leavethebuilding () {...}}

#3. Readresolve method to preserve Singleton property

Private Object readresolve () {    // Return The one true Elvis and let the garbage collector      take care of the Elvis impersonator.    return INSTANCE;}

#4. Enum Singleton-the Preferred Approach

 Public enum Elvis {    INSTANCE;      Public void leavethebuilding () {...}}

Item 4:enforce noninstantiability with a private constructor

Attempting to enforce noninstantiability is making a class abstract does not work.

A class can is made noninstantiable by including a private constructor.

 Public class Utilityclass {    //  Suppress default constructor for noninstantiability    Private  Utilityclass () {        thrownew  assertionerror ();    }     // remainder omitted}    

Java efficient Programming (2)--Creating and destroying Objects