1.考慮用靜態(tài)工廠方法代替構(gòu)造器

靜態(tài)工廠方法慣用名稱

• valueOf —— 類型轉(zhuǎn)換方法

• of —— valueOf的一種更簡(jiǎn)潔的替代

• getInstance —— 該方法沒(méi)有參數(shù)，并返回唯一的實(shí)例

• newInstance —— 確保返回的每個(gè)實(shí)例都與其他實(shí)例不同

• getType —— 與getInstance一樣，但在工廠方法處于不同的類中使用,Type表示工廠方法所返回的對(duì)象類型

• newType —— 與newInstance一樣，但在工廠方法處于不同的類中使用,Type表示工廠方法所返回的對(duì)象類型

• 具體方法參考Boolean，EnumSet

2.遇到多個(gè)構(gòu)造器參數(shù)時(shí)考慮用構(gòu)建器

**代碼實(shí)例 **

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 {
        private int servingSize;
        private 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 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);
        }
    }

    public NutritionFacts(Builder builder) {
        servingSize = builder.servingSize;
        servings = builder.servings;
        calories = builder.calories;
        fat = builder.fat;
        sodium = builder.sodium;
        carbohydrate = builder.carbohydrate;
    }

    public int getServingSize() {
        return servingSize;
    }

    public int getServings() {
        return servings;
    }

    public int getCalories() {
        return calories;
    }

    public int getFat() {
        return fat;
    }

    public int getSodium() {
        return sodium;
    }

    public int getCarbohydrate() {
        return carbohydrate;
    }

    public static void main(String[] args) {
        NutritionFacts nutritionFacts = new Builder(1, 3).calories(2).carbohydrate(2).build();
        System.out.println(nutritionFacts.getCalories());
        System.out.println(nutritionFacts.getCarbohydrate());
        System.out.println(nutritionFacts.getFat());
        System.out.println(nutritionFacts.getServings());
    }
}

3.用私有構(gòu)造器或枚舉類型強(qiáng)化Singleton屬性

代碼實(shí)例

public class Elvis {
    private static final Elvis INSTANCE = new Elvis();
    private Elvis() {}
    private static Elvis getInstance() {
        return  INSTANCE;
    }
}

public enum  Elvis {
    INSTANCE;
}

4.通過(guò)私有構(gòu)造器強(qiáng)化不可實(shí)例化的能力

參考Math，Array，Collections

代碼實(shí)例

public class UnitityClass {
    // 避免調(diào)用構(gòu)造函數(shù)實(shí)例化
    private UnitityClass() {
        throw new AssertionError();
    }
} 

5.避免創(chuàng)建不必要的對(duì)象

代碼實(shí)例

String s = new String("stringtte"); // 不要這樣做

String s = "stringtte";

6.消除過(guò)期的對(duì)象引用

一般而言，只要類是自己管理內(nèi)存，程序員就應(yīng)該警惕內(nèi)存泄露問(wèn)題。

代碼實(shí)例

public Object pop() {
    if (size == 0) {
        throw new EmptyStackException();
    }
    Object result = elements[--size];
    elemtents[size] = null; //重點(diǎn)在這里
    return result;
}