This is essentially what i'm doing
while(true) //cant check for zero, there is more to do here
{
int val = 0;
for(SomeObject i : arrayListOfSomeObjects)
{
if(canDoSomething)
{
val++
}
}
if(val == 0)
{
break;
}
else
{
//do stuff with that nonzero value
}
}
It is strange, because the loop wont yield. As in, stop if unsuccessful. I have a proceedure that will keep going until it finishes, if it does not do anything (or does not meet my conditions in that operation) it wont change the value. Meaning that check on "val" should break the loop. But it doesn't. It just going. I have even printed "val" to the console, yet it returns 0.
At the end of that operation, even if the value IS 0, it keeps going!
Your code is correct.. Try the following..
int val = 1;
while(val>0)
{
//Some operation that will change the value IF successful
}
first int val = 0 supposed to be outside the loop because this will cause the value of the variable val always zero
You might need to make sure you are targeting the 'right' loop by adding a label:
label: while(true) //cant check for zero, there is more to do here
{
// ...
if(val == 0)
{
break label;
}
// ...
}
This will ensure that you break out of the while loop in case the check is in another loop or a switch statement. Otherwise, I am sure that something is causing the problem that you didn't show in your example. Beware of unwanted side-effects.
Related
So I have a loop that is wrapped around a loop and an if statement. When running the program however, it gets out of the inner loop (as planned) and then it fails the if statement (also as planned), resorting to the else statement which is a simple print.
What I /wanted/ to happen was have it then (in the case the if fails), restart to the original inner loop--hence the outer loop. But instead, after it fails the if statement, it begins to loop "phrase2" over and over.
Here is the simplified code:
int x = 1;
int y = 1;
int i = 0;
while(i == 0)
{
while(<condition that is false>)
{
System.out.println("phrase1");
a = input.nextInt();
b = input.nextInt();
}
if(<condition that is false>)
{
i = 1;
}
else
{
System.out.println("phrase2");
}
}
Thanks for your help regardless!
EDIT:
For the sake of emphasis...
What happens:
Infinite loop spewing "phrase2".
What I wanted:
After the else is executed, I wanted to be brought into the inner loop again.
Whatever condition you're using in the inner loop, just make sure it's true.
else
{
System.out.println("phrase2");
// SET THIS TO TRUE: <condition that is false>
}
This way, the inner loop will trigger again.
Your control never enters the below if statement
if(<condition that is false>)
{
i = 1;
}
You might need to adjust your conditions so that it comes into the above if block. Introduce a System.out.println inside if statement to debug
It looks like you have some code that you probably want to run once, unless something went wrong, and then you want to go back and retry. The idiom I usually use for that looks like
boolean needToRetry;
do {
needToRetry = false;
// do whatever
if (somethingWentWrong) {
needToRetry = true;
// set this at any point where you find you will need to go back
}
} while (needToRetry);
The important thing is that you need to reset your flag (needToRetry) at the beginning of the loop, each time. (P.S. There are other ways to do this using break or continue, although I personally don't like using continue.)
I'm making a game where there is a goalie. i want him to move back and forth forever. i have an int called goalieposx (goalie position on the x axis) and i want this is go up by 1 until it hits 200, then go down by one till its back a 0 and repeat. I've tried the folllowing
//this bit isnt in the method, its outside as global varibale
boolean forward=true
//this bit is in a method which is continiouly called nonstop
if (goalieposx<200){
forward=true;
}
else if (goalieposx>200){
forward=false;
}
System.out.println(forward);
if(forward=true){
goalieposx++;
System.out.println("forward");
}
else if (forward=false){
goalieposx--;
System.out.println("backwards");
}
}
this method is called continously. It prints true until it gets to 200, then it prints false. However, it always prints forward, never backward. So conclusion is: the boolean changes as expected but the first if is always called, it seems to ignore the condition
ive also tried this
if(forward = true){
if(goalieposx==200){
forward=false;
}
else{
goalieposx++;}
}
else{
if(goalieposx==0){
forward=true;
}
else{
goalieposx--;}
System.out.println(goalieposx);
}
but this doesnt work either, it prints 1 then 2 etc upto 200 then prints 200 forever. Anyone know how i can solve this? is an if statement the wrong idea altogether?
This is why you should never do comparison for boolean types in if, while, for, whatever. You have just done the assignment in your if statement:
if(forward=true)
the above if statement will always evaluate to true. The problem with this is, this compiles successfully in Java, as syntax wise it's alright. Compiler just checks the type of expression in if evaluates to boolean or not. And it does, so it's ok with it.
You need to do the comparison:
if(forward==true)
.. but as I said, you should not do comparison for boolean types. So, simply doing this:
if(forward)
would be enough.
You also don't need those else if in both the conditions. Just an else will work fine. Well, I don't understand the use of boolean variable at all. It seems like you don't need it. You can change your code to:
if (goalieposx<200){
// forward=true;
goalieposx++;
System.out.println("forward");
}
else {
// forward=false;
goalieposx--;
System.out.println("backwards");
}
What you were previously doing is, setting a boolean variable, based on a condition, and using that boolean variable as condition to execute another if-else block. Well, whatever you are executing in the 2nd if-else block, can simply be moved in the original if-else block, without taking the help of the middle-actor boolean variable.
if(forward=true) does not do what you thing it does.
In java = is the assignment operator and == is the comparison operator. What you are doing with that statement is saying "if assign forward to true" which will set forward to true and always return true.
What you mean to say is if(forward) and if(!forward).
In fact you don't need the else if just an else as if the boolean is not true it must be false.
A better way to do it is to get it to move to the left by adding a minus number, and to the right by adding a positive number. Here's an example of doing this with a loop:
for(int i = -10; i < 100; i++) {
xPosition += i;
}
This would add -10 then -9 etc. to the position.
In your if statements, you need to put two equal signs to check for equality.
if (forward == true){
// execute code
}
EDIT 1:
if (forward)
would be much simpler.
First let's examine what you have already written:
if (goalieposx<200){
forward=true;
}
else if (goalieposx>200){
forward=false;
}
The problem with this code being first is that it while it might set the direction to false once 'goalieposx' has reached 201, in the next call, it will set the direction back to true.
Instead, try using this clever alternative:
//This goes before the infinite loop method
counter = 0;
//Then in the infinite loop method
counter++;
if(counter > 100) {
counter = -100;
}
goalieposx = 100 + counter; //(this shifts counter from
// between -100 and 100 to 0 and 200)
The problem is you are setting the direction based on the value of the integer, instead of whether a condition has previously been met. Try this:
//this bit is in a method which is continiouly called nonstop
if (forward && (goalieposx>200)){
forward=false;
}
System.out.println(forward);
if(forward=true){
goalieposx++;
System.out.println("forward");
}
else if (forward=false){
goalieposx--;
System.out.println("backwards");
}
}
If the die shows a 6, the player doesn't move at all on this turn and also forfeits the next turn.
To accomplish this, I have tried an integer type warning marker variable for the player and an integer type time counter variable.
If the die shows 6, I want to increment the warning marker variable by 1 during the first run(and have the while loop do nothing), then keep the value at 1 during the second run (while loop will not work), then lower it back down to 0 for the third run of the while loop (so the while loop will work). The marker will stay at zero unless the die shows a 6 again, after which the same process will repeat.
I have a while loop like this:
while the warning marker is equal to 0 {
Do Stuff
if the die shows a 6, the warning marker increases by 1.
the time counter also increases by 1.
}
How do I manipulate the variables to get the result that I need? Or is my partially complete method absolutely off in terms of logic?
Thanks.
Can u tell me if this works for you?
flag=true;
while condition{
if flag==true{
if die == 6
{
flag=false;
continue;}
}
else { Do STUFF }
} else
{
flag==true;
}
}
I think you want to reword this problem.
This is what I understood. You have a warning marker.
You have a loop that checks whether the marker is 0, if it is then you do something.
If the die is a six, you will increase the warning marker. If its new value is 3, then you will reset it to 0. Meanwhile, the time counter is always increasing.
If this is correct, I think you want something like:
int warningMarker = 0;
int timeMarker = 0;
while (true) {
if (die == 6) {
++warningMarker;
if (warningMarker == 3) {
warningMarker = 0;
}
}
if (warningMarker == 0) {
doSomething();
}
++timeMarker;
}
Java is Object-Oriented Pragramming language. Use this feature.
See following pseudocode and let me know if you have problem in undestanding it.
Create a class Player as following:
class Player
{
boolean skipChance = false;
... // Other fields
... //
}
Change your while as following:
while(isGameOn())
{
Player p = getCurrentPlayer();
if( ! p.skipChance)
{
int val = p.throwDice();
if(val == 6)
{
p.skipChance = true;
continue; // control moves to while.
}
// Do stuff
}
else
{
p.skipChance = false;
}
}
I've got a bit of an issue with my little program.
I have a JOptionPane asking for a number, and if that number is less than 10, a loop that just continues on and on forever doing what's in it, keeping on asking for numbers. Inside that loop, I call a method, with an int as parameter. In the method, I need to (without altering any of the code in the class that calls the method) find out whether the number I entered is less than 1. If it is, I need to call on another method. That bit's done.
But! The mainloop keeps rolling, so it keeps doing the other stuff in the loop. I need to stop it from doing that, so in the if-statement in the method I need to break that specific iteration of the loop the method is in, and make it go on to a new iteration of the same loop, asking for a new number.
The first class (example):
number=Integer.parseInt( JOptionPane.showInputDialog( "bla bla" ) );
while (number !=- 10) {
themethod(number);
blah
blah
...
}
The called method (example):
public void themethod(int number) {
if (number<1) {
call the other method
break the iteration im in
}
There are a number of things you can do here. Ultimately what you do should depend on your coding style and what you are trying to accomplish.
Option 1 would be some variation of:
for (;;)
{
int number = /* ... */;
myMethod(number);
if (number == -10)
break;
}
You might say, rather subjectively and depending on circumstances, that this is bad, because knowledge of the termination condition is contained in the loop rather than the method doing the "real work". Maybe for your loop that's OK. Maybe in other circumstances (or perhaps with other programmers? This is very much a matter of taste.) you might want to make myMethod make that decision. In general my own personal taste usually leans towards not having scenario knowledge be distributed throughout various methods in source, but in one place.
So most of what I'll write from here on will be how to make myMethod make the decision about whether or not to terminate.
Option 2 - myMethod returns a boolean indicating we should terminate:
for (;;)
{
int number = /* ... */;
if (myMethod(number))
break;
}
boolean myMethod(int number)
{
// TODO - do stuff
return number == -10;
}
But you might say that myMethod already wants to return some other type. I come from very much a C background so the idiom I'm most used to would be the "out parameter". Leading me to option 3:
Option 3 - Out parameter lets caller decide to terminate:
public class CancelIndicator
{
public boolean shouldCancel;
};
CancelIndicator cancel = new CancelIndicator();
while (!cancel.shouldCancel)
{
int number = /* ... */;
myMethod(number, cancel);
}
int myMethod(int number, CancelIndicator cancel)
{
// TODO - do stuff.
cancel.shouldCancel = (number == -10);
return /* ... */;
}
Or maybe you're more a fan of exceptions:
Option 3:
public class CancellationException extends Exception
{
}
try
{
for (;;)
{
int number = /* ... */;
myMethod(numberl);
}
}
catch (CancellationException ex)
{
}
void myMethod(int number) throws CancellationException
{
// TODO - do stuff.
if (number == -10)
throw new CancellationException();
}
As you can see there are a number of options. I'm sure one could spend a whole day talking about different ways to do it. Here is my sample of idioms I have seen - I'll warn you that it's been some time since I've done much in Java so I might not write the most idiomatic code here. :-)
Add a return value indicating that the while should break:
public boolean themethod(int number) {
if(number<1) {
call the other method
return true;
}
return false;
}
Then:
while(number !=-10) {
if(themethod(number)) break;
bla
bla
...
}
Edit: If you can't change the while code, throw an exception from the method:
public void themethod(int number) {
if(number<1) {
call the other method
throw new RuntimeException("Negative Number");
}
}
Wait, so did I get this straight? You have a loop that asks for a number, does something if the number is not -10, and otherwise breaks?
If so, look at this:
while(true) {
number=Integer.parseInt( JOptionPane.showInputDialog( "bla bla" ) );
if(number == -10) {
break;
}
themethod(number);
}
Otherwise, if this is not the case, and you want to break in two cases, the -10 case and the method is false case, you can do this:
Change your method to return a boolean. If it's true, then it doesn't want to break. If it's false then it wants to break, then do this:
while(true) {
number=Integer.parseInt( JOptionPane.showInputDialog( "bla bla" ) );
if(number == -10) {
break;
}
if(!themethod(number)) break;
}
If you really can't edit the loop, then just throw an exception from the method! That will exit your entire program, though. I don't see any other possible way of doing this, however.
Without a return value for themethod(int) and without changing the other class's code, this isn't possible since as it is, there is no return communication. You'll have to change both; it can't be done without changing the logic in the loop.
I want to have a for statement that repeats until a given int reaches a certain value.
For example...
for (int variable = 0; variable < other_variable; variable++) {
The problem with this is that the for statement will never end. It will continue to repeat endlessly. What have I done wrong?
This is my code...
boolean itemexist_check = false;
do {
int i2 = m_area.m_items.size();
for (int i = 0; i < i2; i++) {
String s2 = m_area.m_items.get(i).returnName();
System.out.println("Checking...");
if (s2.contains(s)) {
System.out.println("You take the " + s2 + ".");
itemexist_check = true;
player.addItem(m_area.m_items.get(i));
m_area.m_items.remove(i);
}
else {
//do nothing, repeat loop
}
}
}
while (itemexist_check == false);
In this code, m_area.m_items.size() would return 1, so i2 would be 1.
There are several possibilities:
you change variable inside the body of the loop;
you change other_variable inside the body of the loop;
other_variable is set to a large value, in which case the loop might take a long time to terminate;
your code never completes a certain iteration of the loop, for example:
it's getting stuck inside a nested loop as suggested by #Eng.Fouad in the comments, or
it's waiting for a lock, or
it's blocking inside an I/O call that never completes (or takes a long time to complete) etc.
Without knowing the typical value of other_variable and seeing the body of the loop it's anyone's guess.
On a side note,
String s2 = m_area.m_items.get(i).returnName();
is going to cause an exception if invoked in a subsequent or later repetition after
m_area.m_items.remove(i);
is invoked, because every time m_area.m_items.remove(i) is invoked, the list/array loses an item and its size reduces, which is never reflected in the iteration boundary check.
Surely it is the do/while loop that isn't terminating? That for loop cannot possibly run forever.
You should try a
do {
}while(condition is true)
loop. However that said, you have to implement checks assuming that there will be runaway data or conditions resulting in an infinite loop. Just my 2 cents