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问题，面对这种一个构造器具备多个参数的问题，现有的做法是使用重叠构造器的方式，该方式存在的问题：
public class NutritionFacts {
private final int servingSize; // (mL) required
private final int servings; // (per container) required
private final int calories; // optional
private final int fat; // (g) optional
private final int sodium; // (mg) optional
private final int carbohydrate; // (g) optional
public NutritionFacts( int servingSize, int servings) {
this(servingSize, servings, 0);
}
public NutritionFacts( int servingSize, int servings, int calories) {
this(servingSize, servings, calories, 0);
}
public NutritionFacts( int servingSize, int servings, int calories, int fat) {
this(servingSize, servings, calories, fat, 0);
}
public NutritionFacts( int servingSize, int servings, int calories, int fat,
int sodium) {
this(servingSize, servings, calories, fat, sodium, 0);
}
public NutritionFacts( int servingSize, int servings, int calories, int fat,
int sodium, int carbohydrate) {
this.servingSize = servingSize;
this.servings = servings;
this.calories = calories;
this.fat = fat;
this.sodium = sodium;
this.carbohydrate = carbohydrate;
}
public static void main(String[] args) {
NutritionFacts cocaCola = new NutritionFacts(240, 8, 100, 0, 35, 27);
}
}
重叠构造器存在的问题是，客户端使用NutritionFacts类容易出错，也比较困难，困难在于，客户端要记住构造器的每个参数的含义及顺序。这种方式，可读性也差，原因就是，要读懂一句代码，就要记住该构造器所用所有参数的含义。
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一种替代的解决办法：
public class NutritionFacts {
// Parameters initialized to default values (if any)
private int servingSize = -1; // Required; no default value
private int servings = -1; // " " " "
private int calories = 0;
private int fat = 0;
private int sodium = 0;
private int carbohydrate = 0;
public NutritionFacts() {
}
// Setters
public void setServingSize(int val) {
servingSize = val;
}
public void setServings(int val) {
servings = val;
}
public void setCalories(int val) {
calories = val;
}
public void setFat(int val) {
fat = val;
}
public void setSodium(int val) {
sodium = val;
}
public void setCarbohydrate(int val) {
carbohydrate = val;
}
public static void main(String[] args) {
NutritionFacts cocaCola = new NutritionFacts();
cocaCola.setServingSize(240);
cocaCola.setServings(8);
cocaCola.setCalories(100);
cocaCola.setSodium(35);
cocaCola.setCarbohydrate(27);
}
}
public static void main(String[] args) {
NutritionFacts cocaCola = new NutritionFacts.Builder(240, 8)
.calories(100).sodium(35). carbohydrate(27).build();
}
对比：
public static void main(String[] args) {
NutritionFacts cocaCola = new NutritionFacts(240, 8, 100, 0, 35, 27);
}
JavaBean方式
public static void main(String[] args) {
NutritionFacts cocaCola = new NutritionFacts();
cocaCola.setServingSize(240);
cocaCola.setServings(8);
cocaCola.setCalories(100);
cocaCola.setSodium(35);
cocaCola.setCarbohydrate(27);
}
public class NutritionFacts {
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 {
// Required parameters
private final int servingSize;
private final int servings;
// Optional parameters - initialized to default values
private int calories = 0;
private int fat = 0;
private int carbohydrate = 0;
private int sodium = 0;
public Builder(int servingSize, int servings) {
this.servingSize = servingSize;
this.servings = servings;
}
public Builder calories(int val) {
calories = val;
return this ;
}
public Builder fat(int val) {
fat = val;
return this ;
}
public Builder carbohydrate(int val) {
carbohydrate = val;
return this ;
}
public Builder sodium(int val) {
sodium = val;
return this ;
}
public NutritionFacts build() {
return new NutritionFacts(this);
}
}
private NutritionFacts(Builder builder) {
servingSize = builder.servingSize ;
servings = builder. servings;
calories = builder. calories;
fat = builder. fat;
sodium = builder. sodium;
carbohydrate = builder.carbohydrate ;
}
public static void main(String[] args) {
NutritionFacts cocaCola = new NutritionFacts.Builder(240, 8)
.calories(100).sodium(35).carbohydrate(27).build();
}
}
Item 2---遇到构造器具有多个参数时，要考虑用构建器；Builder模式
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原文地址：http://www.cnblogs.com/ttylinux/p/4354544.html
