Why am I getting a dead code warning on the i++ in this function ?
InputFilter hexInputFilter()
{
return new InputFilter()
{
#Override
public CharSequence filter(CharSequence source, int start,
int end, Spanned dest, int dstart, int dend)
{
for (int i = start; i < end; i++)
{
if ((source.charAt(i) >= '0')
&& (source.charAt(i) <= '9'))
{
return null;
}
if ((Character.toUpperCase(source.charAt(i)) >= 'A')
&& (Character.toUpperCase(source.charAt(i)) <= 'F'))
{
return null;
}
return "";
}
return null;
}
};
}
There's no chance for the for to loop more than once because you are returning:
return "";
Thus, i++ won't be executed ever and that's why you get a dead code warning. Maybe you want to remove that return ""; and/or put it outside the for.
That is because i++ is normally executed after the end of the for-block, and in your function the end of the for-block will never be reached because in the block you unconditionally return a value.
A for-loop
for (A; B; C) {
D;
}
is internally translated into the following:
A;
while (B) {
D;
C;
}
You can see that if D always returns from the function, C will never be reached. That's what the complaint is about.
You'll only ever execute the loop once because of the return ""; statement.
In your case, the below statement is causing the problem as it runs unconditionally and will always run when the for loop is executed. So it will never reach for i++ so its dead code.
return "";
Related
public static boolean hasGreaterDoWhile(List<Integer> numbers, int number) {
int d = 0;
do {
if (numbers.get(d) > number){
return true;
}
d++;
}
while (d < numbers.size());
return false;
}
(JAVA only)
P.s This is a function i have tried, in order to check the first argument, and if it contains a number that is larger than the second argument, it will then return true, and flase otherwise.
Note that it is using do while loop. I just don't know which part of this code i have done wrong, because the system keeps telling me that "java.lang.IndexOutOfBoundsException: Index 0 out of bounds for length 0".
Thank u, any hint will be much appriciated.
your list of Integers is empty. you can't access an index of an empty list:
public static boolean hasGreaterDoWhile(List<Integer> numbers, int number) {
int d = 0;
if (numbers.isEmpty()) return false;
do {
if (numbers.get(d) > number){
return true;
}
d++;
}
while (d < numbers.size());
return false;
}
A do-while control block works as follows:
Execute the do block
Check the condition. If it holds, return to (1)
Notice the order of this flow. Unlike a standard while, do-while will always execute one iteration before checking the condition. Therefore, for an empty list you will always try to access the 0-index element of the table, which does not exist, hence the error. You can use a while loop to avoid this:
public static boolean hasGreaterDoWhile(List<Integer> numbers, int number) {
int d = 0;
while (d < numbers.size()) {
if (numbers.get(d) > number){
return true;
}
d++;
}
return false;
}
You should check whether the collection is empty
like this
if(numbers == null || numbers.isEmpty()) {
return false;
}
int d = 0;
do {
if (numbers.get(d) > number){
return true;
}
d++;
}
while (d < numbers.size());
return false;
What I have so far:
public boolean allSameLetter(String str)
{
for (int i = 1; i < str.length(); i++)
{
int charb4 = i--;
if ( str.charAt(i) != str.charAt(charb4))
{
return false;
}
if ( i == str.length())
{
return true;
}
}
}
Please excuse any inefficiencies if any; still relatively new to coding in general. Am I lacking some knowledge in terms of using operators and .charAt() together? Is it illogical? Or is my error elsewhere?
Using regex:
return str.matches("^(.)\\1*$");
Using streams:
str.chars().allMatch(c -> c == str.charAt(0));
Other:
return str.replace(String.valueOf(str.charAt(0), "").length() == 0;
You can follow the below steps:
(1) Get the first character (i.e., 0th index)
(2) Check the first character is the same with subsequent characters, if not return false (and comes out from method)
(3) If all chars match i.e., processing goes till the end of the method and returns true
public boolean allSameLetter(String str) {
char c1 = str.charAt(0);
for(int i=1;i<str.length;i++) {
char temp = str.charAt(i);
if(c1 != temp) {
//if chars does NOT match,
//just return false from here itself,
//there is no need to verify other chars
return false;
}
}
//As it did NOT return from above if (inside for)
//it means, all chars matched, so return true
return true;
}
As Andrew said, you are decreasing i within your for loop. You can fix this by changing it to int charb4 = i - 1;. As for making your code more efficient you could condense it down to this.
public boolean allSameLetter(String str) {
for(char c : str.toCharArray())
if(c != str.charAt(0)) return false;
return true;
}
Comment if you don't understand a part of it :)
public boolean allSameLetter(String str)
{
for (int i = 1; i < str.length() -1; i++)
{
if ( str.charAt(i) != str.charAt(i+1))
{
return false;
}
}
return true
}
-1 is there since I am checking the current value in the array, then the next value in the array, thus I need to stop a place earlier.
If the loop if statement is never entered, it will make it far enough into the code to return true
You have to create a for loop that searches through the length of the String - 1. this way the program will not crash because of a 3 letter word with the program trying to get the 4th letter. This is what works for me:
public boolean allSameLetter(String str)
{
for(int i = 0; i< str.length()-1; i++){
if (str.charAt(i) != str.charAt(i+1)){
return false;
}
}
return true;
}
if((new HashSet<Character>(Arrays.asList(s.toCharArray()))).size()==1)
return true;
return false;
This should be enough
The bug is caused by
int charb4 = i--;
this line is equal to
int charb4 = i-1;
i=i-1;
Because of this, your loop will never stop.
The easiest way to fix this
public boolean allSameLetter(String str)
{
for (int i = 1; i < str.length(); i++)
{
if ( str.charAt(i) != str.charAt(i-1))
{
return false;
}
}
}
I want to return Vector according to if block but the code gives me the following error: Add return statement.
Is it possible to write return statement in if block?
public static int[] zeroVectorBinning1( ImageFloat32 angle,ImageFloat32 Magnitude )
{
for (int NumberOFChanks=0;NumberOFChanks<locations_original.size();NumberOFChanks++)
{
for(int i=0;i<angle.getHeight();i++)
for(int j=0;j<angle.getWidth();j++)
{
int orientaionVal=(int) angle.get(j, i);
if(orientaionVal<=0)
{int magnitudeVal=(int) Magnitude.get(j, i);
int[] Vector = new int[19];
Vector=zeroVector(19);
Vector[0]=magnitudeVal;
return Vector;
}
else if(orientaionVal<=20)
{int magnitudeVal=(int) Magnitude.get(j, i);
int[] Vector = new int[19];
Vector=zeroVector(19);
Vector[1]=magnitudeVal;
return Vector;
}
else(orientaionVal >= 0 && orientaionVal <=20)
{
int magnitudeVal=(int) Magnitude.get(j, i);
int[] Vector = new int[19];
Vector=zeroVector(19);
Vector[0]=magnitudeVal;
Vector[1]=magnitudeVal;
return Vector;
}
}
}
}
There's nothing wrong in having return statements in if blocks, but your method must have a return statement in any execution path.
Your for loops may never be executed (if, for example, locations_original.size() is 0), in which case none of the if blocks that contain the return statements will be reached. Therefore you must add a return statement following the loops.
Yes,
But your function still not return anything in the end, so you have to return something, even null.
So when you call this function, it should ne looking like this:
int[] fuctionResult = zeroVectorBinning1(....);
if (fuctionResult != null){
....
}
You could resolve this in two ways:
At the end either throw an exception just before completing the method.
Or at the end just return null.
Reason why compiler is complaining because, if locations_original.size() returns 0 then this method would never return anything which contradicts with what you said in your method that it will return an int array.
It is possible. But you need a return statement for every cases. Also if your for loop is never executed.
so add return null; at the end of your method.
Yes it is possible. Follow the code snippet for explanation.
public class TestSample {
public static void main(String... w){
int h = new TestSample().call();
System.out.println(h);
}
public int call(){
int j =0;
for(int i=0;i<10;i++){
if(i==5){
return i;
}
}
return j;
}
}
This prints 5.
public int getValue(){
final int value = 3;
if(value==1){
return 1;
}
else if(value==2){
return 2;
}
else if(value==3){
return 3;
}
else{
return -1;
}
// no return because "else" covers all cases
}
In this case you have an "else" at the end, so every case is covered. but if you leave the else ...
public int getValue(){
final int value = 3;
if(value==1){
return 1;
}
else if(value==2){
return 2;
}
else if(value==3){
return 3;
}
return -1;
// ... you have to return something at the end of the method, because value could be >3 or < 1 and the code under the last else if will be executed
}
The problem is your if/else-if/else parse is not complete, what does else with a condition like:
else(orientaionVal >= 0 && orientaionVal <=20)
mean? It's odd. Just omit the condition (orientaionVal >= 0 && orientaionVal <=20) of the last else sentence (and it's not logically correct when orientaionVal is 0 or 20), or there will be no default else in the scope.
When return in the scope of a if sentence, we must make sure that under any condition there is a return, so:
Make a default return out of the if-else scope
Or be sure that the condition judgement is complete and there is a return under any condition.
So
Correct:
if(condition){
return;
}
return;
Correct:
if(condition){
return;
}else if(anotherCondition){
return;
}else{
return;
}
Wrong:
if(condition){
return;
}
// no return ...
Wrong:
if(condition){
return;
}else if(anotherCodition){
return;
}
// no return ...
I have a method that takes an array as a parameter and returns a boolean.
Inside the method, I have an if/else statement. If the statement is true, I want the result to return true, if the statement is false, I want the statement to returns false.
public static boolean allPositive (double[] arr)
{
for (int i = 0; i < arr.length; i++)
{
if(arr[i] > 0)
{
return true;
}
else
{
return false;
}
}
return //What do i put here?
}
}
Of course, it needs a return value at the end. However, I am confused on what I should return at the bottom. How should I rewrite this?
First, your code is wrong. For example, with {1, -1, 2}, your method will return true.
If you write it differently, you avoid the problem :
public static boolean allPositive (double[] arr) {
for (int i = 0; i < arr.length; i++) {
if(arr[i] < 0)
{
return false;
}
}
return true;
}
EDIT : Or even better, a one-line solution with Java 8 and Streams (I like one-line solutions):
public static boolean allPositive (double[] arr) {
//Stream the array and see if any elements matches condition `<0`.
return !Arrays.stream(arr).anyMatch(i->i<0);
}
If you need more than one line of code in order to work with collections, then you should learn about Streams.
public static boolean allPositive (double[] arr)
{
boolean b = true;
for (int i = 0; i < arr.length; i++)
{
if(!(arr[i] > 0))
{
b = false;
}
}
return b;
}
The way Java works, it ensures no problems with your code by making sure all your returns happen outside of the if else statement. This because, a common bug by programmers is to return in the if else statement, but never create an else condition, so the method never returns anything. Doing it this way is more of a good practice thing so you don't bug out later trying to figure out why a method won't return.
The answer by Arnaud has multiple return statements. Code smell. The answer by DreadHeadedDeveloper has a logic error if the array is {1,-1,2}, it returns true.
This function/method is terse and follows good coding practices.
public static boolean allPositive (double[] arr) {
boolean ret = true;
for (int i = 0; i < arr.length; i++) {
if(arr[i] <= 0) {
ret = false;
}
}
return ret;
}
You have to return in the end of the method (after the loop) the value that should be returned if an empty array is passed to your method. It's up to you to decide whether an empty array is "allPositive" or not.
Okay, so my question is regarding boolean returns. For my Comp Sci homework, I have to make a course registration program using methods, and one of them is an add course method. Basically, you search for the class in a catalog, and if it matches you add it to the students schedule and return a boolean value of true. I did this, but for some reason it is giving me an error. Here is the code:
public static boolean addCourse(
Course[] catalog,
Course[] mySchedule,
int myNumCourses,
int dept,
int courseNum)
{
int j;
int i;
int k;
int deptCat;
int courseNumCat;
Course courseAdd = null;
char checkDay;
int checkTime;
if (mySchedule.length == myNumCourses) {
return false;
}
for (i = 0 ; i < catalog.length ; i++) {
Course course = catalog[i];
deptCat = course.getDepartment();
courseNumCat = course.getCourseNumber();
if (deptCat == dept && courseNumCat == courseNum) {
courseAdd = catalog[i];
break;
}
else continue; }
for (j = 0 ; j < myNumCourses ; j++) {
if (mySchedule[j] == null) {
mySchedule[j] = courseAdd;
return true;
}
else continue;
}
for (k = 0 ; k < mySchedule.length ; k++) {
Course course = mySchedule[k];
if (course != null) {
checkDay = course.getDay();
checkTime = course.getPeriod();
if (checkDay == courseAdd.getDay() && checkTime == courseAdd.getPeriod()) {
return false;
}
}
else continue;
}
}
Why doesn't it recognize the boolean return values? Is it because I placed them inside a loop?
You need to place a return-statement at the end of your method, even if you might know it will never be reached (the compiler is not smart enough to know that, which explains the error).
For instance, even this will not compile:
public static boolean foo() {
if (true)
return true;
}
unless we add a final return statement. What you have is analogous.
There is nothing wrong with putting your return values in loops, however, the compiler sees no guarantee that this method will return a value and thus raises an error. At the very end of the method you need to return either true or false, whichever is most appropriate. All of your returns are within conditionals and therefor could fail to execute leaving your function with no return statement.
You must explicitly return a boolean(true/false) in ALL code path.Because your function's return type is "boolean".
In your case,you must add a return statement after the last loop.
If you don't want to write to many "return xx" statement,you can change the return type of this function to "void".And throw Exception in the false cases.
I think there is a problem with the last loop. If the condition for returning false is never met, it continues until it get to the end of the schedule, without returning anything. If you were to add a return at the end of the method this loop could fall through to it. Did you mean to return true after the loop, if no 'return false' is executed?
for (k = 0; k < mySchedule.length; k++) {
Course course = mySchedule[k];
if (course != null) {
checkDay = course.getDay();
checkTime = course.getPeriod();
if (checkDay == courseAdd.getDay()
&& checkTime == courseAdd.getPeriod()) {
return false;
}
} else
continue;
}
Where ever you are using if statement its possible else also must return or flow must go to another return.ELSE is missing with return.