Effective Java English Second Edition reading note Item 2:consider a builder when faced with many constructor parameters.

 PackageBuildermanypara;//JavaBeans pattern-allows inconsistency,mandates mutability Public classNutritionfactsbean {//Parameters initialized to default values (if any)//Required    Private intServingsize =-1; Private intServings =-1; //option    Private intCalories = 0; Private intFat = 0; Private intSodium = 0; Private intCarbohydrate = 0;  PublicNutritionfactsbean (intServingsize,intservings) {        Super();  This. servingsize =servingsize;  This. servings =servings; }     Public intgetservingsize () {returnservingsize; }     Public voidSetservingsize (intservingsize) {         This. servingsize =servingsize; }     Public intgetservings () {returnservings; }     Public voidSetservings (intservings) {         This. servings =servings; }     Public intgetcalories () {returncalories; }     Public voidSetcalories (intcalories) {         This. Calories =calories; }     Public intGetfat () {returnfat; }     Public voidSetfat (intfat) {         This. Fat =fat; }     Public intGetsodium () {returnsodium; }     Public voidSetsodium (intsodium) {         This. sodium =sodium; }     Public intgetcarbohydrate () {returncarbohydrate; }     Public voidSetcarbohydrate (intcarbohydrate) {         This. Carbohydrate =carbohydrate; }     Public Static voidMain (string[] args) {Nutritionfactsbean Nutritionfactsbean=NewNutritionfactsbean (240, 8); Nutritionfactsbean.setfat (8); }}

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

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

 PackageBuildermanypara;//Builder Pattern Public classNutritionfactsbuilder {Private Final intservingsize; Private Final intservings; Private Final intcalories; Private Final intfat; Private Final intsodium; Private Final intcarbohydrate;  Public Static classBuilderImplementsBuilders<nutritionfactsbuilder> {        //Required Parameters        Private Final intservingsize; Private Final intservings; //Optional parameters-initialized to default values        Private intCalories = 0; Private intFat = 0; Private intSodium = 0; Private intCarbohydrate = 0;  PublicBuilder (intServingsize,intservings) {            Super();  This. servingsize =servingsize;  This. servings =servings; }         PublicBuilder Calories (intcalories) {             This. Calories =calories; return  This; }         PublicBuilder Fat (intfat) {             This. Fat =fat; return  This; }         PublicBuilder Sodium (intsodium) {             This. sodium =sodium; return  This; }         PublicBuilder Carbohydrate (intcarbohydrate) {             This. Carbohydrate =carbohydrate; return  This; }         PublicNutritionfactsbuilder Build () {return NewNutritionfactsbuilder ( This); }    }    PrivateNutritionfactsbuilder (Builder builder) {Servingsize=builder.servingsize; Servings=builder.servings; Calories=builder.calories; Fat=Builder.fat; Sodium=Builder.sodium; Carbohydrate=builder.carbohydrate; }     Public Static voidMain (string[] args) {Nutritionfactsbuilder nutritionfacts=NewNutritionfactsbuilder.builder (240, 8). Calories (). Sodium (35). build (); }}

 Package Buildermanypara; // A Builder for objects of type  Public Interface Builders<t> {    public  T Build ();}

In summary,the Builder pattern was a good choice when designing classes whose constructors or static factories would Ore than a handful of parameters,especially if most of those parameters is optional. Client code is much easier to read and write with builders than with the traditional telescoping constructor Pattern,and b Uilders is much safer than JavaBeans.

Effective Java English Second Edition reading note Item 2:consider a builder when faced with many constructor parameters.