Hey Builder
Wealth is the test of a man’s character.–财富是对一个人品格的试金石.
大家都知道,静态工厂和构造器有个共同的局限性,就是它们不能很好地扩展到大量的可选参数,因此有什么办法实现呢？
那就是Builder模式,它既能保证像重叠构造器模式那样的安全性,也能像JavaBean那样有着良好的可读性,它的使用,就是不直接产生对象,而是让客户端利用所有必要的参数调用构造器,得到一个Builder对象,然后客户端zai builder对象上调用类似于setter的方法,来设置每个相关的参数,最后,客户端调用无参数的builder方法,来生产不可变得对象,这个builder就是它构建的类的静态成员类.
爱码如下:
public class NutritionFacts {
// required 必选参数
private final int servingSize;
private final int servings;
// 可选参数
private final int calories;
private final int fat;
private final int sodium;
private final int color;
@Override
public String toString() {
return "NutritionFacts{" +
"servingSize=" + servingSize +
", servings=" + servings +
", calories=" + calories +
", fat=" + fat +
", sodium=" + sodium +
", color=" + color +
'}';
}
// 静态内部类 Builder构建器
public static class Builder{
// required
private final int servingSize;
private final int servings;
// Optional 给出默认值
private int calories = 0;
private int fat = 0;
private int sodium = 0;
private int color = 0;
// Builder 构造方法 含有必选参数
public Builder(int servingSize, int servings) {
this.servingSize = servingSize;
this.servings = servings;
}
// 构建方法
public Builder calories(int val){
calories = val;
return this;
}
public Builder fat(int val){
fat = val;
return this;
}
public Builder sodium(int val){
sodium = val;
return this;
}
public Builder color(int val){
color = val;
return this;
}
public NutritionFacts build(){
return new NutritionFacts(this);
}
}
// 目标类的构造方法
public NutritionFacts(Builder builder) {
servingSize = builder.servingSize;
servings = builder.servings;
calories = builder.calories;
fat = builder.fat;
sodium = builder.sodium;
color = builder.color;
}
public static void main(String[] args) {
// 测试 可选参数
NutritionFacts nutritionFacts = new NutritionFacts(new Builder(240,90 ).calories(20).sodium(40).color(89));
System.out.println(nutritionFacts.toString());
}
}
测试结果:
NutritionFacts{servingSize=240, servings=90, calories=20, fat=0, sodium=40, color=89}
是不是感觉很简单呢?
