不可變對象在多線程的情形下是線程安全的。構建規則可參照如下代碼中註釋。

//類添加final修飾符，保證類不被繼承
public final class ImmutableNutritionFacts {
    //所有成員變量必須私有，並且加上final修飾
    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 final List<String> list;

    //通過構造器初始化所有成員，進行深拷貝(deep copy)
    public ImmutableNutritionFacts(int servingSize, int servings, int calories, int fat,
                                   int sodium, int carbohydrate, List<String> list){
        this.servingSize = servingSize;
        
 
this.servings = servings;
        this.calories = calories;
        this.fat = fat;
        this.sodium = sodium;
        this.carbohydrate = carbohydrate;
        this.list = list.subList(0, list.size()); //deep copy(引用類型)
    }
    //不提供改變成員變量的方法，包括setter
    //在getter方法中，不要直接返回對象本身，而是克隆對象，並返回對象的拷貝
    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 List<String> getList() {
        return list.subList(0, list.size()); //返回對象的拷貝
    }
}

不可變對象