I have to fill in an ArrayList with the first 10 multiples of two using a for each loop. I really can't seem to figure out how and I can't use any other loops.
Here is my code which is not working.
ArrayList<Integer> arraylist = new ArrayList<Integer>(10);
for (Integer y : arraylist) {
arraylist.add( (2+(y*2)));
}
I'll address the point that everyone here is mostly glossing over: there is a key difference between a normal for statement and the enhanced-for statement.
The enhanced-for is defined in the JLS as syntactic sugar. What kind of sugar you get depends on what you're iterating over.
If you're iterating over an Iterable like an ArrayList, it is using the Iterator from that entity.
for(I #i=Expression.iterator(); #i.hasNext();){
VariableModifiersopt TargetType Identifier=
(TargetType) #i.next();
Statement
}
If you're iterating over an array, then it's shorthand for the common for statements one is accustomed to doing.
T[] #a = Expression;
L1: L2: ... Lm:
for (int #i = 0; #i < #a.length; #i++) {
VariableModifiersopt TargetType Identifier = #a[#i];
Statement
}
Thus, the enhanced-for has one assumption:
The statement is only meant to iterate over existing elements, not provide a way or interface to iteratively add new elements.
There are any number of ways to sort this out, but the simplest is the most common approach: use a for statement.
ArrayList<Integer> arraylist = new ArrayList<Integer>(10);
for (int i = 0; i < 10; i++) {
arraylist.add( (2+(i*2)));
}
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