Chapter 2: create and destroy objects. Item2: when encountering multiple constructors, consider using the builder.

If a class contains a large number of optional parameters, you can use the following methods:

1. Overlapping constructor:

Package com. twoslow. cha2;/*** the overlapped constructor is feasible, but it is difficult to write client code when many parameters are involved. * @ Author sai **/public class item201 {private final int servingsize; private final int servings; private final int Calories; private final int fat; private final int sodium; private Final int Carbohydrate; Public item201 (INT servingsize, int servings) {This (servingsize, servings, 0);} public item201 (INT servingsize, int servings, int calories) {This (servingsize, servings, calories, 0);} public item201 (INT servingsize, int servings, int calories, int fat) {This (servingsize, servings, calories, fat, 0);} public item201 (INT servingsize, int servings, int calories, int fat, int carbohydrate) {This (servingsize, servings, calories, fat, carbohydrate, 0 );} public item201 (INT servingsize, int servings, int calories, int fat, int carbohydrate, int sodium) {This. servingsize = servingsize; this. servings = servings; this. calories = Calories; this. fat = fat; this. carbohydrate = Carbohydrate; this. sodium = sodium ;}}

2. The JavaBeans mode provides the setter method:

Package com. twoslow. cha2;/*** JavaBeans mode. Call the setter method to set each required parameter. * The constructor is divided into several calls. During the constructor, the JavaBean may be inconsistent. * @ Author sai **/public class item202 {private int servingsize =-1; private int servings =-1; private int calories = 0; private int fat = 0; private int sodium = 0; private int carbohydrate = 0; Public item202 () {} public void setservingsize (INT servingsize) {This. servingsize = servingsize;} public void setservings (INT servings) {This. servings = servings;} public void setcalories (INT calories) {This. calories = Calories;} public void setfat (INT fat) {This. fat = fat;} public void setsodium (INT sodium) {This. sodium = sodium;} public void setcarbohydrate (INT carbohydrate) {This. carbohydrate = Carbohydrate ;}}

3. Builder:

Package com. twoslow. cha2;/*** builder, not enough: 1. To create an object, you must explicitly create its builder. * 2. It is more lengthy than the overlapped constructor and can only be used when there are many parameters,> = 4. * @ author sai **/public class item203 {private final int servingsize; private final int servings; private final int Calories; private final int fat; private final int sodium; private Final int Carbohydrate; public static class builder {// builder private final int servingsize; private final int servings; private int calories = 0 can be constructed through the implementation of generic interfaces; private int fat = 0; private int sodium = 0; private int carbohydrate = 0; Public Builder (INT servingsize, int servings) {This. servingsize = servingsize; this. servings = servings;} public builder calories (INT calories) {This. calories = Calories; return this;} public builder fat (INT fat) {This. fat = fat; return this;} public builder sodium (INT sodium) {This. sodium = sodium; return this;} public builder carbohydrate (INT carbohydrate) {This. carbohydrate = Carbohydrate; return this;} public item203 build () {return New item203 (this) ;}} public item203 (Builder) {This. servingsize = builder. servingsize; this. servings = builder. servings; this. calories = builder. calories; this. fat = builder. fat; this. sodium = builder. sodium; this. carbohydrate = builder. carbohydrate ;}}

 

Chapter 2: create and destroy objects. Item2: when encountering multiple constructors, consider using the builder.