Java reflection - use of array class

It goes without saying that everyone knows java.lang.Array It's right Java A class that reflects array operations in a package .JavaSE8 In your document Array My description goes like this ：

The Array class provides static methods to dynamically create and access Java arrays.

Array Class provides static methods for dynamic creation and access Java Array . Access is not difficult to understand , Dynamic creation can take a closer look at .

Let's see first java.util.Arrays

• Note that Arrays, I believe some friends have used this tool class many times , It provides many methods for array operation, which is convenient for us to use .

• It says java.lang.Array It provides us with static methods to dynamically create and access arrays . Let's see Arrays Medium copyOf How to dynamically manipulate arrays .

copyOf What is it for ？Arrays This method is mainly provided to expand the size of the filled array .

You can use

  I don't know if you've noticed , This method is a generic return result . Its first argument is the original array , The second parameter is the new length , Returns a call to another overloaded copyOf Method , Let's take a look at this overloaded copyOf Methods! .

• The call inside is not difficult to understand , If it comes in original Object array Class and Object[] Of Class Equal, then directly new Object[] If not, call java.lang.reflect.Array Medium newInstance Method to create a new array , The next call is System.arraycopy Method, the comments in the source code are ：Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array. intend ： Copy from the specified position of the specified array to the specified position of the target array .

Why use reflection to expand arrays

• Let's take a look at the implementation without reflection "copyOf"

• Without the one above Arrays Of copyOf Many people may write the above code directly . But have you ever thought about a question , Can it be transformed into the corresponding class you want to use ？ Say so , One MyObject[] Class into Object[], Then it's OK to turn back , But from the beginning Object[] The array of cannot be converted to MyObject[], Doing so will throw ClassCastException abnormal , This is because this array uses new Object[length] Created ,Java When creating an array, remember the type of each element , Is in the new The type of time .

• So how can we make a strong turn ？ Look at the code below

Read the code above , Some friends will have questions , Why use object Receive array objects , This is because arrays of basic data types cannot be passed to object arrays , But it can be turned into an object

Access the objects in the array

• Array Class provides some methods for us to use

 

  The complete code is as follows