Builder模式，不直接生成想要的对象，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。然后客户端在builder对象上调用类似于setter的方法，
来设置每个相关可选的参数，最后调用无参的build来生成不可变的对象。
完整代码+测试：github:完整代码+测试
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| 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;
private NutritionFacts(Builder builder) {
servingSize = builder.servingSize;
servings = builder.servings;
calories = builder.calories;
fat = builder.fat;
sodium = builder.sodium;
carbohydrate = builder.carbohydrate;
}
public static class Builder {
private final int servingSize;
private final int servings;
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) {
this.fat = val;
return this;
}
public Builder carbohydrate(int val) {
this.carbohydrate = val;
return this;
}
public Builder sodium(int val) {
this.sodium = val;
return this;
}
public NutritionFacts build() {
return new NutritionFacts(this);
}
}
@Override
public String toString() {
return "NutritionFacts{" +
"servingSize=" + servingSize +
", servings=" + servings +
", calories=" + calories +
", fat=" + fat +
", sodium=" + sodium +
", carbohydrate=" + carbohydrate +
'}';
}
}
|