本篇內(nèi)容來(lái)自于個(gè)人在學(xué)習(xí)《effective java》一書(shū)時(shí)的理解咕痛，記錄下自己的學(xué)習(xí)情況

1. 重疊構(gòu)造器

public class NutritionFactsConstructor {
    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 NutritionFactsConstructor(int servingSize, int servings){
        this(servingSize, servings, 0);
    }
    public NutritionFactsConstructor(int servingSize, int servings, int calories){
        this(servingSize, servings, calories, 0);
    }
    public NutritionFactsConstructor(int servingSize, int servings, int calories, int fat){
        this(servingSize, servings, calories, fat, 0);
    }
    public NutritionFactsConstructor(int servingSize, int servings, int calories, int fat, int sodium){
        this(servingSize, servings, calories, fat, sodium, 0);
    }
    public NutritionFactsConstructor(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;
    }
}

缺點(diǎn)： 在使用時(shí)簿姨，當(dāng)選擇在參數(shù)列表中位置靠后的可選參數(shù)時(shí)距误，必須同時(shí)給必選參數(shù)和選擇的最后一個(gè)可選參數(shù)之間的無(wú)關(guān)參數(shù)賦值。

測(cè)試：

NutritionFactsConstructor n1 = new NutritionFactsConstructor(1, 1);
NutritionFactsConstructor n2 = new NutritionFactsConstructor(1, 2, 6);
NutritionFactsConstructor n3 = new NutritionFactsConstructor(1, 3, 0, 5);
System.out.println("n1 = " + n1 + "\nn2 = " + n2 + "\nn3 = " + n3);
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輸出：
n1 = NutritionFactsConstructor{servingSize=1, servings=1, calories=0, fat=0, sodium=0, carbohydrate=0}
n2 = NutritionFactsConstructor{servingSize=1, servings=2, calories=6, fat=0, sodium=0, carbohydrate=0}
n3 = NutritionFactsConstructor{servingSize=1, servings=3, calories=0, fat=5, sodium=0, carbohydrate=0}

2. JavaBeans

public class NutritionFactsJavaBeans {
    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 NutritionFactsJavaBeans(int servingSize, int servings){
        this.servingSize = servingSize;
        this.servings = servings;
    }

    @Override
    public String toString() {
        return "NutritionFactsJavaBeans{" +
                "servingSize=" + servingSize +
                ", servings=" + servings +
                ", calories=" + calories +
                ", fat=" + fat +
                ", sodium=" + sodium +
                ", carbohydrate=" + carbohydrate +
                '}';
    }

    public int getServingSize() {
        return servingSize;
    }

    public void setServingSize(int servingSize) {
        this.servingSize = servingSize;
    }

    public int getServings() {
        return servings;
    }

    public void setServings(int servings) {
        this.servings = servings;
    }

    public int getCalories() {
        return calories;
    }

    public void setCalories(int calories) {
        this.calories = calories;
    }

    public int getFat() {
        return fat;
    }

    public void setFat(int fat) {
        this.fat = fat;
    }

    public int getSodium() {
        return sodium;
    }

    public void setSodium(int sodium) {
        this.sodium = sodium;
    }

    public int getCarbohydrate() {
        return carbohydrate;
    }

    public void setCarbohydrate(int carbohydrate) {
        this.carbohydrate = carbohydrate;
    }
}

特點(diǎn)：通過(guò)構(gòu)造器給必選參數(shù)賦值扁位，然后使用setter方法來(lái)給需要的可選參數(shù)賦值准潭。
缺點(diǎn)：該種方法無(wú)法實(shí)現(xiàn)類的不可變性。
測(cè)試：

NutritionFactsJavaBeans n1 = new NutritionFactsJavaBeans(1, 1);
n1.setFat(1);
n1.setCarbohydrate(5);
System.out.println(n1);
------------------------------------------------------------------------------------------------
輸出：
NutritionFactsJavaBeans{servingSize=1, servings=1, calories=0, fat=1, sodium=0, carbohydrate=5}

3. 構(gòu)建器

public class NutritionFactsBuilder {
    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 NutritionFactsBuilder(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;
    }

    @Override
    public String toString() {
        return "NutritionFactsBuilder{" +
                "servingSize=" + servingSize +
                ", servings=" + servings +
                ", calories=" + calories +
                ", fat=" + fat +
                ", sodium=" + sodium +
                ", carbohydrate=" + carbohydrate +
                '}';
    }

    public static class Builder{
        private final int servingSize;
        private final int servings;
        private int calories;
        private int fat;
        private int sodium;
        private int carbohydrate;

        public Builder(int servingSize, int servings){
            this.servingSize = servingSize;
            this.servings = servings;
        }

        public Builder calories(int value){
            this.calories = value;
            return this;
        }
        public Builder fat(int value){
            this.fat = value;
            return this;
        }
        public Builder sodium(int value){
            this.sodium = value;
            return this;
        }
        public Builder carbohydrate(int value){
            this.carbohydrate = value;
            return this;
        }

        public NutritionFactsBuilder build(){
            return new NutritionFactsBuilder(this);
        }
    }
}

特點(diǎn)：先實(shí)例化靜態(tài)內(nèi)部類的對(duì)象域仇，設(shè)定好參數(shù)后再通過(guò)build方法調(diào)用外部類的構(gòu)造器從而返回外部類的對(duì)象刑然。在使用方法上具有非常好的可讀性。
缺點(diǎn)：在非常追求性能優(yōu)化時(shí)暇务，靜態(tài)內(nèi)部類可能會(huì)影響性能泼掠。

測(cè)試：

NutritionFactsBuilder n1 = new NutritionFactsBuilder.Builder(1, 1).calories(1).carbohydrate(1).build();
NutritionFactsBuilder n2 = new NutritionFactsBuilder.Builder(2,2).fat(1).sodium(1).build();
System.out.println(n1);
System.out.println(n2);
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輸出：
NutritionFactsBuilder{servingSize=1, servings=1, calories=1, fat=0, sodium=0, carbohydrate=1}
NutritionFactsBuilder{servingSize=2, servings=2, calories=0, fat=1, sodium=1, carbohydrate=0}