The code below doesn’t do what I expect. Every string is null after this code executes.
String[] currentState = new String[answer.length()];
for(String x : currentState)
{
x = "_";
}
The code below does what I expect. Every string in currentState is now “_”
String[] currentState = new String[answer.length()];
for (int i = 0; i < currentState.length; i++) {
currentState[i] = "_";
}
Can someone explain why the first case doesn’t work?
By design the for each variable ‘x’ (in this case) is not meant to be assigned to. I’m surprised that it even compiles fine.
String[] currentState = new String[answer.length()];
for (String x : currentState) {
x = "_"; // x is not a reference to some element of currentState
}
The following code maybe shows what you’re in effect are doing. Note that this is not how enumerations work but it exemplifies why you can’t assign ‘x’. It’s a copy of the element at location ‘i’. (Edit: note that the element is a reference type, as such it’s a copy of that reference, assignment to that copy does not update the same memory location i.e. the element at location ‘i’)
String[] currentState = new String[answer.length()];
for (int i = 0; i < answer.length(); i++) {
String x = currentState[i];
x = "_";
}
Answer：
Original code:
String currentState = new String[answer.length()];
for(String x : currentState)
{
x = "_";
}
Rewritten code:
String currentState = new String[answer.length()];
for(int i = 0; i < currentState.length; i++)
{
String x;
x = currentState[i];
x = "_";
}
How I would write the code:
String currentState = new String[answer.length()];
for(final String x : currentState)
{
x = "_"; // compiler error
}
Rewritten code with the error:
String currentState = new String[answer.length()];
for(int i = 0; i < currentState.length; i++)
{
final String x;
x = currentState[i];
x = "_"; // compiler error
}
Making the variables final highlights when you do things like this (it is a common beginner mistake). Try to make all of your variables final (instance, class, arguments, exceptions in catch. etc…) – only make them non-final if you really have to change them. You should find that 90%-95% of your variables are final (beginners will wind up with 20%-50% when they start doing this).
Answer：
Because x is a reference (or a variable of reference-type). All the first piece of code does is re-point the reference at a new value. For example
String y = "Jim";
String x = y;
y = "Bob";
System.out.println(x); //prints Jim
System.out.println(y); //prints Bob
The fact that you are re-assigning the reference y to “Bob” does not affect what the reference x was assigned to.
Answer：
You can convert your array to a List and then iterate like this:
String[] currentState = new String[answer.length()];
List<String> list = Arrays.asList(currentState);
for(String string : list) {
x = "_";
}
Answer：
Object x[]={1,”ram”,30000f,35,”account”};
for(Object i:x)
System.out.println(i);
for each is used for sequential access
Answer：
The for each loop meant for this:
List suits = ...;
List ranks = ...;
List sortedDeck = new ArrayList();
for (Suit suit : suits){
for (Rank rank : ranks)
sortedDeck.add(new Card(suit, rank));
}
so consider above you can do this:
String[] currentState = new String[answer.length()];
List<String> buffList = new ArrayList<>();
for (String x : currentState){
x = "_";
buffList.add(x);
// buffList.add(x = "_" ); will be work too
}
currentState = buffList.toArray(currentState);