重用构造函数和最终实例字段

Question

让我们假设我有以下类试图成为不可变的

    public class Computation {

    private final Operation operation;
    private final double epsilon;

    public Computation(Operation operation) {
        this.operation = operation;
        //Default value
        epsilon = 0.01;

    }


    public Computation(Operation operation double epsilon) {
        this(operation);
        //Won't compile as epsilon is final and is set by the other constructor
        this.epsilon = epsilon;
    }
}

而且,为了这个问题,让我们假设我不想在这个类中使用构建器(这将解决问题).

所以问题是:

有没有办法实现这种行为,而无需将最终修饰符移除到epsilon并保留两个构造函数？

也就是说,没有做类似的事情

       public class Computation {

        private final Operation operation;
        private final double epsilon;

        public Computation(Operation operation Double epsilon) {
            this(operation);
            this.epsilon = (epsilon == null) ? 0.01 : epsilon;
        }
    }

而不使用建设者

   public class Computation {

    private final Operation operation;
    private final double epsilon;

    private Computation(Builder builder) {
        this.operation = builder.operation;
        this.epsilon = builder.epsilon;

    }


    public static class Builder {

    private final Operation operation;
    //Default value
    private double epsilon = 0.01;

    public Builder(Operation operation) {
        this.operation = operation;
    }

    public Builder epsilon(double epsilon) {
         this.epsilon = epsilon;
         return this;
    }

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

}

Answer 1

是 - 反转逻辑,以便具有较少参数的构造函数调用具有更多参数的构造函数:

public Computation(Operation operation) {
    this(operation, 0.01);
}

public Computation(Operation operation, double epsilon) {
    this.operation = operation;
    this.epsilon = epsilon;
}

基本上这样你就可以得到很多构造函数,这些构造函数都只是委托给一个完成所有实际工作的"真正"构造函数.