effective java-讀書筆記
阿新 • • 發佈:2022-01-11
遇到引數過多可以考慮建造者模式,在構造器中傳入建造器,在建造器裡面初始化引數,這樣可以防止構造器引數過多傳錯了
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(); } }
另外一種方法,使用set的方法設定值,
容易導致javaBean處於不穩定的狀態,多執行緒下可能出現值錯誤
警惕自動裝箱帶來的效能損耗
如果將Long sum = 0L; 換成long sum = 0L;在資料量大時提升效能很明顯 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."); } } }