首页 > 代码库 > 第二章：创建和销毁对象。ITEM2：遇到多个构造器参数时要考虑用构建器。
第二章：创建和销毁对象。ITEM2：遇到多个构造器参数时要考虑用构建器。
如果一个类中有大量的可选参数，有以下几种方式：
1、重叠构造器：
package com.twoslow.cha2;/** * 重叠构造器可行，但是当由许多参数的时候，客户端代码很难编写。 * @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、javaBeans模式，提供setter方法：
package com.twoslow.cha2;/** * JavaBeans模式，调用setter方法设置每个必要的参数。 * 构造过程被分到了几个调用中，在构造过程中JavaBean可能处于不一致的状态。 * @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、构建器：
package com.twoslow.cha2;/** * 构建器，不足：1、为了创建对象，必须显创建它的构建器。 * 2、比重叠构造器更加冗长，只在有很多参数的时候才使用，>=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 {//可以通过实现泛型接口构建任何类型的Builder private final int servingSize ; private final int servings ; private int calories = 0; 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 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 ; }}
第二章：创建和销毁对象。ITEM2：遇到多个构造器参数时要考虑用构建器。
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