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Orici
Asked: 2020-03-08 04:08:50 +0800 CST 2020-03-08 04:08:50 +0800 CST

Initialize Java Arrays

  • 772

Why doesn't the following work to initialize an array?

public class TestArrays {

    private static int[] numbers;
    public static void main(String[] args) {

        numbers = {1,2,3}; //error
    }
} //class

but yes in this way?

public class TestArrays {

    private static int[] numbers;
    public static void main(String[] args) {

        int[] arr = {1,2,3};
        numbers = arr;
    }
} //class
java

2 Answers

  1. Best Answer

    Java allows you to initialize an array using curly braces as follows:

    int [] array = new int[] {1,2,3};

    Said format, only in the case that we are declaring the variable , can be simplified to

    int [] array = {1,2,3};

    Instead, the first way does work without a declaration:

    int array[];
array= new int[] {1,2,3};

    Why? Well, aside from why it's defined that way in the language specs, we'd have to ask its creator to find out why he restricted the short form to variable declarations. My opinion is that, if we admit the following:

    int [] array = {1,2,3};
array = {2,3,43};

    It would not be totally clear if in the second assignment we are creating a new array of the same size or if we are replacing the values ​​in the object (array) that already existed. By forcing ourselves to put new int[], the doubt is clarified.

    • 15

  2. To complement @Pablo Lozano's answer. The java specification states the correct syntax and where it is used, in the following paragraphs:

    JLS 10.6 :

    An array initializer may be specified in a declaration (§8.3, §9.3, §14.4), or as part of an array creation expression (§15.10), to create an array and provide some initial values.

    Which in Spanish would be:

    An array initializer can be specified in a declaration (§8.3, §9.3, §14.4), or as part of an array creation expression (§15.10), to create an array and provide some initial values.

    Where they define the initializer array as:

    ArrayInitializer:
    { VariableInitializersopt ,opt }

VariableInitializers:
    VariableInitializer
    VariableInitializers , VariableInitializer

    Where an array creation expression is defined as:

    ArrayCreationExpression:
    new PrimitiveType DimExprs Dimsopt
    new ClassOrInterfaceType DimExprs Dimsopt
    new PrimitiveType Dims ArrayInitializer 
    new ClassOrInterfaceType Dims ArrayInitializer

DimExprs:
    DimExpr
    DimExprs DimExpr

DimExpr:
    [ Expression ]

Dims:
    [ ]
    Dims [ ]
    • 3