如何在Java中调整数组大小？

Question

As the title, how can I resize array in java, without importing any library, including ArrayList , Arrays.copyOf ...etc.

Also, I have to resize again and again in my program, with the unknown input data.( ie I have a small array, but when the data increasing, how can I resize it? )

Answer 1

Java does not have a "resize" option for allocated storage. You must allocate new storage of the required size and copy the data from the old storage to the new.

You can use System.arraycopy() to copy the data. The ArrayList and Vector classes automatically perform these reallocate and copy operations, so if you don't use them, you are reinventing the wheel.

java.lang.System is, of course, automatically imported into every java program, so, as required, you don't need import java.lang.System; to implement this.

Answer 2

Unfortunately, you cant resize an array in java .

Some things you could do are:

1. When new data is taken in, make a new array and copy the old array + the new data.

2. Use an ArrayList which makes the array bigger as you add data to it.

3. Use java.util.Arrays.copyOf(...) . This returns a bigger array with the contents of the previous array.

Answer 3

a array is by definition fixed in size, I know many modern languages let you assign the length and change the length dynamically

but I think what you are looking for is a Vector

https://docs.oracle.com/javase/7/docs/api/java/util/Vector.html

it allows O(1) access (like the array) while beeing dynamic in length

Answer 4

You can not increase the size of an array once it is declared. So you have to use Collection framework in java, may be ArrayList or LinkedList.

That is what is the difference between Array and ArrayList. In ArrayList you can add element dynamically,no need to increase it's size.