Consider the following Java code:
int[] array = {1, 2, 3, 4, 5, 6};
for(int i : array) {
System.out.print(i + " ");
}
The above code obviously prints the contents of the array.
1 2 3 4 5
My question is why doesn't Java allow this?
int[] array = {1, 2, 3, 4, 5, 6};
int i;
for(i : array) {
System.out.print(i + " ");
}
EDIT: when I compile the 2nd program, I get the following error:
Main.java:14: error: bad initializer for for-loop
for(i : array) {
^
1 error
Because Java forces you to declare a variable here. The JLS, Section 14.14.2, defines the enhanced for loop with syntax:
EnhancedForStatement:
for ( {VariableModifier} UnannType VariableDeclaratorId : Expression ) StatementEnhancedForStatementNoShortIf:
for ( {VariableModifier} UnannType VariableDeclaratorId : Expression ) StatementNoShortIf
The UnannType is a type for the variable being declared.
It goes on to state that such an enhanced for loop is the equivalent of this, for looping over Iterables...
for (I #i = Expression.iterator(); #i.hasNext(); ) {
{VariableModifier} TargetType Identifier =
(TargetType) #i.next();
Statement
}
... and for arrays...
T[] #a = Expression;
L1: L2: ... Lm:
for (int #i = 0; #i < #a.length; #i++) {
{VariableModifier} TargetType Identifier = #a[#i];
Statement
}
It's clear that the variable is a locally declared variable inside the loop.
What is the error showing? Maybe you should initialize the varible:
int i = 0;
for-loop also changes the value of that int right away, so initializing that variable does not change anything.
You are using “Enhanced” for-loops. This is a feature available after Java 1.5. The syntax of enhanced for loop is
for(Object obj : List) {
...
}
If you write in other format it will throw a compilation error. Basically the code you wrote is syntactically incorrect. This will be a compilation error.
You can refer What is the syntax of enhanced for loop in Java?
Iterableinterface, specifically forgetting toimplementsit. The Java 1.5.0 "For-Each Loop" docs it links to also don't mention it, although all their examples match his first version, they don't rule out his second.