是否可以在Java中创建泛型的2D锯齿状数组？

Question

Is it possible to create an two-dimensional array of a generic type parameter with only a size specified in Java?

To illustrate, can we create an array like this:

T[][] array = new T[x][];

Answer 1

You mention "generic" in your question and use the identifier T for your type, so I'm going to assume you are talking about creating an array of a generic type parameter.

You can't do that in Java. Arrays and generics don't mix very well. You can do it with reflection ( see this question ) but you might have an easier time doing this with a collection class instead. It would be a List of Lists, to get a 2D ragged container.

Answer 2

Not with generics, but using a known class it is possible. For generic i would recommend using ArrayList or similar.

 String[][] array = new String[2][];

It can be used in this way:

array[0] = new String[1];
array[1] = new String[4];
array[0][0] = "Hello 0,0";
array[1][1] = "Hello 1,1 ";

System.out.println(array[0][0]);
System.out.println(array[1][1]);

Answer 3

You want a generic multidimensional array. You cannot create one. However, you can create an Object array and then cast it. This is the "usual" way of creating generic arrays:

@SuppressWarnings("unchecked")
T[][] array = (T[][])new Object[x][];

You need @SuppressWarnings("unchecked") because the cast is not safe and checked. From a typetheoretic point of view, it is even "wrong" (an array of type Object is NOT an array of T ), but Java's type system has this inconsistency and this is the way to handle it.