对象缓存技术

Question

假设我有A、B、C类。C有一个方法longRunningMethod，它需要很长时间才能运行并返回int。类A和B都有C作为依赖项，并且需要调用方法longRunningMethod。

public class A{
    private C c;
    public A(C c){
        this.c = c;
    }
    
    public void method1(){
        this.c.longRunningMethod();
    }
}

public class B{
    private C c;
    public A(C c){
        this.c = c;
    }
    
    public void method2(){
        this.c.longRunningMethod();
    }
}

public class C{
    
    public int longRunningMethod(){
        ...
    }
}

public class MyProgram{

    public static void main(String[] args){
        C c = new C();
        A a = new A(c);
        B b = new B(c);
        a.method1();
        b.method2()//avoid calling c.longRunningMethod();
    }
}

可以采取哪些方法来避免两次调用longRunningMethod？当然，简单的方法是将A和B的构造函数参数更改为int，并在MyProgram中调用longRunningMethod。但是，传递给A和B的内容并不那么明显(哪些int是允许的？)

Answer 1

public class C{
    private boolean wasCalled = false;
    private int cachedValue;

    public int longRunningMethod(){
        if (!wasCalled) {
            // do your long running job here and set result to cachedValue
            wasCalled = true;
        }
        return cachedValue;
    }
}