I'm trying to write a method that looks through an array of objects for a certain color, which is also an object.
public Ghost findFirst(Color c){
for (int i=0;i<ghosts.length;i++) {
if (ghosts[i].getColor()==c)
return ghosts[i];
else
return null;
}
}
So if the color of a certain ghost matches color c, then return that ghost. However, I'm getting a dead code warning for i++. Whats wrong with my code? Oh also I'm getting a method error saying this function should return a ghost. I thought I am?
Because you return from the loop on the first iteration! So "i" never gets incremented. Either remove the else block completely or change the "return null" to "continue".
As a separate point, the == is checking referential equality, not object equality. It seems likely you should be using ".equals" instead
fixed code:
public Ghost findFirst(Color c){
for (int i=0;i<ghosts.length;i++) {
if (ghosts[i].getColor().equals(c))
return ghosts[i];
}
return null;
}
keep in mind that return terminates the function (including the loop obviously). So if you found the right color ghost - you return it (thus ending your search and never reaching the return null; line). If your for loop found nothing - you get to the last line and return null.
Its because of
else
return null;
!
Because of that return-Statement your Loop will only be executed once.
public Ghost findFirst(Color c){
for (int i=0; i < ghosts.length; i++) {
if (ghosts[i].getColor().equals(c))
return ghosts[i];
}
return null;
}
If I 'unroll' your loop, the code does something like:
public Ghost findFirst(Color c){
if (ghosts[0].getColor()==c)
return ghosts[0];
else
return null;
if (ghosts[1].getColor()==c)
return ghosts[1];
else
return null;
if (ghosts[2].getColor()==c)
return ghosts[2];
else
return null;
//etc...
}
Should be clear from this, that it will never reach the second if, it returns (breaks out of the function) at the first if, true or false.
Your multiple return may be a problem. Sometime it makes it simpler to have one return.
public Ghost findFirst(Color c) {
Color color = null;
for (int i=0;i<ghosts.length;i++) {
if (ghosts[i].getColor().equals(c))
color = ghosts[i];
}
return color;
}
Related
is it possible by any means in the following method that the print statement get executed after the if statement returns true in the for loop?
public boolean contains(Object o) {
if(o == null){
throw new IllegalArgumentException();
}
for(int i = 0; i < size(); i++){
if(o.equals(getNodeAt(i).data)){
System.out.println("contains passed here: "+o+" "+getNodeAt(i)+" "+i);
return true;
}
System.out.println(getNodeAt(1));
}
System.out.println("cointain failed here "+o);
return false;
}
Of course; call the method again. More effectively, efficiently, and specifically with an Object such that o.equals(getNodeAt(i).data is false. The truth is...
"[B]y any means" is a pretty loose constraint; you say...
is it possible by any means in the following method that the print statement get[s] executed after the if statement returns true in the for loop?
I'm saying that YES, that's possible by any means when the means are recalling the method. In fact, it's perpetually true as long as you're using whatever container.
Proof:
Assume that it is impossible by any means in the following method that the second return statement gets executed after the if statement returns true in the for loop.
static String proof(Object o) {
for(int i = 0; i < 1; ++i) {
if (o == null) {
return "I'm returning from the for loop!!!";
}
}
return "I'm now called after the for's return statement (by any means)!! - QED";
}
But given...
public static void main(String...args) {
System.out.println(proof(null));
System.out.println(proof(new String("Hello Proof!")));
}// end main method
the ouput is...
I'm returning from the for loop!!!
I'm now called after the for's return statement!! - QED
Therefore our assumption is wrong and it is possible by some means for the second return statement to get executed after the if statement returns true in the for loop.
;)
A "better" way to phrase that so it's clear what you're asking would be, perhaps, - "Is it possible for the code in a method body to continue to execute after a return statement?"
That answer is no and can be tested in any good IDE as follows.
static String proof(Object o) {
for(;;)
if(true)
return "Donkey Butts";
return "Poops";
}
This basically says forever it is true that I will return "Donkey Butts". In any IDE I'd waste my time using you will get an error for "unreachable statement". The IDE can determine this truth from your code which implicitly is telling you that any time the loop is active and the if is true the code below cannot execute.
No, it is definitely not possible.
No, but it is possible that System.out isn't flushed until after the return statement.
Yes, if you enclose in a try and finally.
public boolean contains(Object o) {
if(o == null){
throw new IllegalArgumentException();
}
for(int i = 0; i < size(); i++){
try {
if(o.equals(getNodeAt(i).data)){
System.out.println("contains passed here: "+o+" "+getNodeAt(i)+" "+i);
return true;
}
} finally {
System.out.println(getNodeAt(1));
}
}
System.out.println("cointain failed here "+o);
return false;
}
Nothing inside a method can be executed after the return statement.
But when you deal with output operations, things can happen quite differently from what you might expect. In fact, writes to an output file/device are often buffered, i.e. written to an internal array. When the array is full, it is sent to the file/device. This happens for efficiency reasons, because writing a few big chunks of data is faster than writing lots of small ones.
This means that these operations sometimes seem to happen long after the place where they appear in the code.
I'm trying to create a recall program that sends text messages to 200+ people and then searches an email that the replies are forwarded too.
This method is supposed to search the array list of replies that is built using another method, but it doesn't work correctly. It will only work if the very first message on the array list matches the very first number in the contact list.
Those are some other problems, but my main question here is why does it say that the code specifically inside of my for loop is dead code?
public static boolean searchForPhone(String phone){
CharSequence phoneN = phone;
for(int i=0;i<myMessages.size();i++){
if(myMessages.get(i).contains(phone)){
return true;
}
else{
return false;
}
}
return false;
}
This is your code, properly formatted:
public static boolean searchForPhone(String phone) {
for (int i = 0; i < myMessages.size(); i++) {
if (myMessages.get(i).contains(phone)) {
return true;
} else {
return false;
}
}
return false;
}
The construct flagged as Dead code is the i++ in the for-loop header. It is indeed dead code because the for loop's body unconditionally makes the method return. Therefore the "step" part of the for header is unreachable aka. dead.
The same fact makes your code perform incorrectly, BTW. Removing the else clause would be a big improvement.
Will this help?
public static boolean searchForPhone(String phone){
CharSequence phoneN = phone;
for(int i=0;i<myMessages.size();i++){
if(myMessages.get(i).contains(phone)){
return true;
}
}
return false;
}
Look you are looping over n-element list. When you get first element on the list you got if/else statement.
So you will HAVE TO either of 2 things, both of witch is return. So your program will exit on first element returned.
To make it simplier, your code is equal to:
CharSequence phoneN = phone;
if (myMessages.size() ==0 ){
return false;
}
return myMessages.get(0).contains(phone);
Try from Window > Preferences > Java > Compiler > Error/Warnings
Change Dead code (e.g 'if(false)') and Unnecessary 'else' statement to Error.
Your loop always returns from the function at the end of the first iteration. This makes i++ dead code since it never executes.
Anyway, remove the else clause to fix the code.
In the else part you need to continue to search. Else if your fist element is not the matching one will return false and not going to check other element.
public static boolean searchForPhone(String phone) {
CharSequence phoneN = phone;
for (int i = 0; i < myMessages.size(); i++) {
if (myMessages.get(i).contains(phone)) {
return true;
} else {
//return false this conditional return cause
// the complain it as dead code. Since for loop will become not
//loop
continue; // will search for other elements.
}
}
return false;
}
Now you can simplify this code to following because else part is not really necessary.
public static boolean searchForPhone(String phone) {
CharSequence phoneN = phone;
for (int i = 0; i < myMessages.size(); i++) {
if (myMessages.get(i).contains(phone)) {
return true;
}
}
return false;
}
Eclipse keeps telling me to add a return statement to the method, even though I did so.
public class PrefixCode {
public String isOne(String[] words) {
if(words.length==1) {
return "Yes";
}
ArrayList<Integer> indexPositions= new ArrayList<Integer>();
for(int i=0;i<words.length;i++) {
String firstWord=words[i];
java.util.List<String> listOfWordsToCheck = new ArrayList<String>(Arrays.asList(words));
listOfWordsToCheck.set(i,null);
for(int j=0;j<listOfWordsToCheck.size();j++) {
String secondWord= listOfWordsToCheck.get(j);
if(firstWord.startsWith(secondWord)==true) {
indexPositions.add(j);
}
else if(firstWord.startsWith(secondWord)==false);
}
}
if(indexPositions.size()==0) {
return "Yes";
}
else if(indexPositions.size()!=0) {
Collections.sort(indexPositions);
return "No,"+indexPositions.get(0)+"";
}
}
}
My return statements are outside of the for loops, so I don't understand what's wrong here.
There is no default return. The only returns you are making are if some conditions are true. What if the conditions are false?
Add a return after the last else block and you are all good to go.
The else block is redundant. What lies inside the else block should be be without else.
Since you have added if, else if, you need to else to that control flow to satisfy the compiler. Logically, size can be either zero or more than zero. So, you need to have if and else part only
if(indexPositions.size()==0){
return "Yes";
} else if(indexPositions.size()!=0){
Collections.sort(indexPositions);
return "No,"+indexPositions.get(0)+"";
} else {
// return what?
}
You can simplify this logic by,
if(indexPositions.size() == 0) {
return "Yes";
} else { //size more than zero
Collections.sort(indexPositions);
return "No,"+indexPositions.get(0) + "";
}
you should use else instead of
else if(indexPositions.size() != 0) {
Collections.sort(indexPositions);
return "No,"+indexPositions.get(0) + "";
}
The compiler doesn't know if the if conditions are going to succeed. So, you need to add a default return out of those if (even if your if conditions cover all possible cases!)
One of the best practice is to have only one return at the method end! Like this:
public String isOne(String[] words) {
String isOne = null;
if(words.length==1){
isOne = "Yes";
}
...
if(indexPositions.size()==0){
isOne = "Yes";
}
else if(indexPositions.size()!=0){
Collections.sort(indexPositions);
isOne = "No,"+indexPositions.get(0)+"";
}
return isOne;
}
Sometimes you may initialize the variable with a default value too, even if in this case is not needed :
String isOne = "No";
In also in your code there is an "error", the indexPositions.size may only be 0 or more, so you may want to use else instead of else if, and complete the graph. In this case eclipse won't tell you to add a return statement anymore, even if you use the return inside the condition block.
if(indexPositions.size()==0) {
return "Yes";
}
else {
Collections.sort(indexPositions);
return "No,"+indexPositions.get(0)+"";
}
I usually do this by declaring a boolean at the start of the function and set it to false. If for whatever reason the function says that variable is gonna be true. I set the declared variable to true instead of returning true. At the end of the function i return that declared variable.
It then has its default return and if the variable was set to true, it returns true.
I'm trying to make a boolean method, but it's not recognizing I have a return statement. What should I do?
public boolean isThreeKind( int rankHist[]) {
for (int i=0;i<=13;i++){
if (rankHist[i]>=3){
return true;
}else{
return false;
}
}
}
Your code does not make sense. There is no point in having a loop if you're always going to run the code inside the loop exactly once. I think you must have misunderstood. What are you trying to do?
Assuming the method only has to return true or false if it is greater than equal to 3,
would recommend to keep it simple.
Also, Please Note:
Loop through the i=0 to i< rankHist.length incase the array contains less than 13 elements you will encounter an ArrayOutOfBoundException.
If it contains more than 13 elements, the output might be incorrect.
.
public boolean isThreeKind( int rankHist[]) {
for (int i=0;i<rankHist.length;i++){
if (rankHist[i]>=3){
return true;
}
}
return false;
}
I think what he wants is if every element in the 13 are >=3, he should return a true, else ways he should return a false.
public boolean isThreeKind( int rankHist[])
{
for (int i=0;i<=13;i++)
{
if (rankHist[i]<3)
{
return false; // Will return false if either of the element have value <3
}
}
return true; // Will return true only if all the 13 elements have value >=3
}
This is literally what your code is doing right now:
public boolean isThreeKind( int rankHist[]) {
return rankHist[0] >= 3;
}
That is it, and I am assuming this is not what you are attempting to do. So if you tell us what you are actually trying to accomplish we can help you more.
In java, You always gotta keep track of returning something EVERYWHERE the method can exit. If it can exit without hitting a return statement, you'll see that error.
So, for your code, to modify it and make it see it, you would need to have it say:
public boolean isThreeKind( int rankHist[]) {
for (int i=0;i<=13;i++){
if (rankHist[i]>=3){
return true;
}else{
return false;
}
}
return false;
}
Or true, if you would rather that.
You should avoid multiple return statement.
You can use a flag. Declare the flag outside the for loop, then assign the value accordingly, and do not miss the break statement.
Do it like that:
public boolean isThreeKind( int rankHist[]) {
boolean value = false;
for (int i=0;i<=13;i++){
if (rankHist[i]>=3){
value = true;
break;
}
}
return value;
}
I get an error in the code from this part of my code:
public boolean findCustomer(String inPersonalNumber){
// check if personal number already exist
for (int i=0; i<customerList.size();i++) {
if(customerList.get(i).getCustomerPersonalNumber().equals(inPersonalNumber)){
return true;
}
}
return true;
}
When I remove the first return true and instead to the last return true, it don't get the error in my eclipse code, but why can't I have the first place and would this be the same? Thanks!
EDIT: The error message from eclipse say: This method must return a result of type boolean. I'm confused because isn't that what I have done?!
Yes, a break must be in the code
Can I write the method in some other way?
EDIT NUMBER 2
Why isn't this code working?
public boolean findCustomer(String inPersonalNumber){
// check if personal number already exist
for (int i=0; i<customerList.size();i++) {
if(customerList.get(i).getCustomerPersonalNumber().equals(inPersonalNumber)){
return true;
}
else {
return false;
}
}
}
This method returns a boolean value so I don't understand why I get an error!? The code looks right to me?
Your edit #2 doesn't compile because there is a possibility that your code won't enter the for-loop. This will be the case if customerList.size() is 0. To fix this, you'll simply need to add a return statement after the for-loop as well:
// check if personal number already exist
for (int i=0; i<customerList.size();i++) {
if(customerList.get(i).getCustomerPersonalNumber().equals(inPersonalNumber)){
return true;
}
else {
return false;
}
}
return false;
Another point here is that this code doesn't logically make much sense: it will only return true or false based on the first item in your list. And this is probably not what you want. So take a closer look at several of the other answer here, many of which are good examples for how you can do this.
public boolean findCustomer(String inPersonalNumber){
boolean result = false;
// check if personal number already exist
for (int i=0; i<customerList.size();i++) {
if(customerList.get(i).getCustomerPersonalNumber().equals(inPersonalNumber)){
result = true;
break;
}
}
return result ;
}
When I remove the first return true and instead to the last return
true, it don't get the error in my eclipse code, but why can't I have
the first place and would this be the same?
If you remove the second return statement the code would be able to run and not return a value - this is not possible as you defined the method to have a return type of Boolean. So it must always return a value no matter what.
Just change the second return statement to false, should do what you want.
Looks like you have turned off the Build Automatically feature of eclipse. It maybe complaining about an error that used to be present when you still hadn't typed in your code fully! This can also happen if you have back-dated your system for some reason.
Also, shouldn't you be returning false if the condition doesn't satisfy?
public boolean findCustomer(String inPersonalNumber) {
// check if personal number already exist
for (int i = 0; i < customerList.size(); i++) {
if (customerList.get(i).getCustomerPersonalNumber().equals(inPersonalNumber)) {
return true;
}
}
return false;
}
First return will return only in case of all conditions satisfied, but this method should be returning boolean as per code. It would be expecting a return in failure case also.
Removing first return won't affect compilation as it has a return in second place which will work without any condtions.
Edit : Answer for your second question
This code has two return's, but what if your customerList is size 0, in that case also, method must return boolean. right? for that only, compiler is asking.
BTW, code doesn't have null checks.
Your final code could be this. Keeping multiple return statements in code in not a good practice.
public boolean findCustomer(String inPersonalNumber) {
boolean retVal = false;
if (!(inPersonalNumber == null || inPersonalNumber.trim().equals("")
|| customerList == null || customerList.size() == 0)) { // inputs are valid to run this check
// check if personal number already exist
for (int i = 0; i < customerList.size(); i++) {
if (inPersonalNumber.equals(customerList.get(i).getCustomerPersonalNumber()) { // to avoid NPE, kept inPersonalNumber in check
retVal = true;
break;
}
}
}
return retVal;
}
Because your for loop looses meaning if you're returning true anyway.
If you want to stop loop use break; instead of first return.