How is this illegal

Question

a) int i[] = new int[2]{1,2};
b) int[] i = new int[]{1,2,3}{4,5,6}; 

I know we cannot give size of an array at declaration . But in statement(a) we

Answer 1

Why not consult the Java Language Specification?

JLS 15.10 - Array Creation Expressions

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 [ ]

Notice that this means that array creation expressions with initializers can only have empty brackets.

Array initializers are defined in 10.6

ArrayInitializer:
{ VariableInitializersopt ,opt }

VariableInitializers:
VariableInitializer
VariableInitializers , VariableInitializer

The following is repeated from §8.3 to make the presentation here clearer:
VariableInitializer:
Expression
ArrayInitializer