Effective Java

public class Test1 {

    public static void main(String[] args) {

        BigInteger bigInteger = BigInteger.probablePrime(10, new Random());
        System.out.println(bigInteger);

        Boolean.valueOf("true");

        Integer.valueOf(1);
    }

}

public class Test2 {

    public static void main(String[] args) {
        NutritionFacts21 nutritionFacts = new NutritionFacts21.Builder(240, 8).calories(100).sodium(35).carbohydrate(27).build();

    }
}


public class NutritionFacts21 {

    private final int servingSize;
    private final int servings;
    private final int calories;
    private final int fat;
    private final int carbohydrate;
    private final int sodium;

    public static class Builder implements javafx.util.Builder<NutritionFacts21> {
        // Requied parameters
        private final int servingSize;
        private final int servings;
        // Optional parameters
        private int calories = 0;
        private int fat = 0;
        private int carbohydrate = 0;
        private int sodium = 0;

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

        public NutritionFacts21 build() {
            return new NutritionFacts21(this);
        }

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

    private NutritionFacts21(Builder builder) {
        servingSize = builder.servingSize;
        servings = builder.servings;
        calories = builder.calories;
        fat = builder.fat;
        carbohydrate = builder.carbohydrate;
        sodium = builder.sodium;
    }

}

public class Elvis31 implements Serializable {

    private static final long serialVersionUID = -8522463178624169893L;

    private static final Elvis31 INSTANCE = new Elvis31();


    private Elvis31() {

    }

    public static Elvis31 getInstance() {
        return INSTANCE;
    }

//    private Object readResolve() {
//        return  INSTANCE;
//    }

}



public enum Elvis32 {

    INSTANCE;

}


public class Test3 {

    public static void main(String[] args) throws Exception {
        Elvis31 elvis311 = Elvis31.getInstance();
        Elvis31 elvis312 = Elvis31.getInstance();
        System.out.println(elvis311 == elvis312);

        FileOutputStream fos1 = new FileOutputStream("a.txt");
        ObjectOutputStream oos1 = new ObjectOutputStream(fos1);
        oos1.writeObject(elvis311);
        oos1.flush();
        oos1.close();

        FileInputStream fis1 = new FileInputStream("a.txt");
        ObjectInputStream ois1 = new ObjectInputStream(fis1);
        Elvis31 elvis313 = (Elvis31) ois1.readObject();

        System.out.println(elvis311 == elvis313);


        //

        Elvis32 elvis321 = Elvis32.INSTANCE;
        Elvis32 elvis322 = Elvis32.INSTANCE;
        System.out.println(elvis321 == elvis322);

        FileOutputStream fos2 = new FileOutputStream("a.txt");
        ObjectOutputStream oos2 = new ObjectOutputStream(fos2);
        oos2.writeObject(elvis321);
        oos2.flush();
        oos2.close();

        FileInputStream fis2 = new FileInputStream("a.txt");
        ObjectInputStream ois2 = new ObjectInputStream(fis2);
        Elvis32 elvis323 = (Elvis32) ois2.readObject();

        System.out.println(elvis321 == elvis323);

    }
}

参考：https://blog.youkuaiyun.com/qq_25827845/article/details/85016496