Why Can't I Initialize an Undeclared Array in Java?

Array Initialization Syntax and Declaration Constraints

In Java, there are various ways to initialize arrays, but they must adhere to specific syntax rules. This article addresses why the Java compiler restricts initializing an array variable that has not been declared.

When declaring an array, it is possible to simultaneously initialize it with values using curly brackets. For instance, the following code is valid:

AClass[] array = {object1, object2};

Another option is to create the array using the new keyword and then assign values to its elements individually:

AClass[] array = new AClass[2];
...
array[0] = object1;
array[1] = object2;

However, the following code is not allowed by the Java compiler:

AClass[] array;
...
array = {object1, object2};

This restriction arises from the requirement that arrays must be declared before they can be initialized. In the above code, the array variable array is declared without specifying its size or initializing it. As a result, Java does not allow the direct assignment of values using curly brackets.

The Java designers' motivation for this restriction is unknown. However, the rule ensures consistency in the language syntax and prevents potential ambiguities during code interpretation.

Although this restriction may sometimes introduce additional code, it can be bypassed by using the following syntax:

AClass[] array;
...
array = new AClass[]{object1, object2};

This method declares the array variable without initialization and then initializes it later using the new keyword and curly brackets.

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