Java遍历整数数组

Question

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

Answer 1

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 ) Statement 

EnhancedForStatementNoShortIf:

 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 Iterable s...

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.

Answer 2

What is the error showing? Maybe you should initialize the varible:

int i = 0;

Answer 3

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?