effective java-读书笔记

本文主要是介绍effective java-读书笔记，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！

遇到参数过多可以考虑建造者模式,在构造器中传入建造器,在建造器里面初始化参数,这样可以防止构造器参数过多传错了

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 {
        // Required parameters
        private final int servingSize;
        private final int servings;

        // Optional parameters - initialized to default values
        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 sodium(int val)
        { sodium = val;        return this; }
        public Builder carbohydrate(int val)
        { carbohydrate = val;  return this; }

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

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

    public static void main(String[] args) {
        NutritionFacts cocaCola = new NutritionFacts.Builder(240, 8)
                .calories(100).sodium(35).carbohydrate(27).build();
    }
}

另外一种方法,使用set的方法设置值,
容易导致javaBean处于不稳定的状态,多线程下可能出现值错误

警惕自动装箱带来的性能损耗

如果将Long sum = 0L; 换成long sum = 0L;在数据量大时提升性能很明显
public class Sum {
    private static Long sum() {
        Long sum = 0L;
        for (long i = 0; i <= Integer.MAX_VALUE; i++)
            sum += i;
        return sum;
    }

    public static void main(String[] args) {
        int numSets = 10;
        long x = 0;

        for (int i = 0; i < numSets; i++) {
            long start = System.nanoTime();
            x += sum();
            long end = System.nanoTime();
            System.out.println((end - start) / 1_000_000. + " ms.");
        }


    }
}

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