java.lang.class学习2--获取构造方法的过程,

最新推荐文章于 2024-03-28 00:08:51 发布

aliahhqcheng

最新推荐文章于 2024-03-28 00:08:51 发布

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分类专栏：开源jar包学习学习分享文章标签：获取构造方法的过程

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本文深入探讨了Java反射机制中构造方法的获取与复制过程。通过分析privateGetDeclaredConstructors和getConstructor0方法的具体实现，揭示了如何根据参数类型获取特定构造方法的内部逻辑。此外，还介绍了软引用缓存机制在提高反射效率方面的作用。

    private Constructor<T> getConstructor0(Class[] parameterTypes,
                                        int which) throws NoSuchMethodException
    {
        Constructor[] constructors = privateGetDeclaredConstructors((which == Member.PUBLIC)); //获取public的构造方法
        for (int i = 0; i < constructors.length; i++) {
            if (arrayContentsEq(parameterTypes,
                                constructors[i].getParameterTypes())) {
                return getReflectionFactory().copyConstructor(constructors[i]); //返回构造方法的对象
            }
        }
        throw new NoSuchMethodException(getName() + ".<init>" + argumentTypesToString(parameterTypes));
    }

    //
    // Other helpers and base implementation
    //

    private static boolean arrayContentsEq(Object[] a1, Object[] a2) {
        if (a1 == null) {//比较构造方法的参数
            return a2 == null || a2.length == 0;
        }

        if (a2 == null) {
            return a1.length == 0;
        }

        if (a1.length != a2.length) {
            return false;
        }

        for (int i = 0; i < a1.length; i++) {
            if (a1[i] != a2[i]) {
                return false;
            }
        }

        return true;
    }



 //
    //
    // java.lang.reflect.Constructor handling
    //
    //

    // Returns an array of "root" constructors. These Constructor
    // objects must NOT be propagated to the outside world, but must
    // instead be copied via ReflectionFactory.copyConstructor.
    private Constructor[] privateGetDeclaredConstructors(boolean publicOnly) {
        checkInitted();
        Constructor[] res = null;
        if (useCaches) {
            clearCachesOnClassRedefinition();
            if (publicOnly) {
                if (publicConstructors != null) {
                    res = (Constructor[]) publicConstructors.get();
                }
            } else {
                if (declaredConstructors != null) {
                    res = (Constructor[]) declaredConstructors.get();
                }
            }
            if (res != null) return res;
        }
        // No cached value available; request value from VM
        if (isInterface()) {
            res = new Constructor[0];
        } else {
            res = getDeclaredConstructors0(publicOnly); //本地方法，获取声明的构造方法
        }
        if (useCaches) {
            if (publicOnly) {
                publicConstructors = new SoftReference(res);
            } else {
                declaredConstructors = new SoftReference(res);
            }
        }
        return res;
    }