I'm taking an intro to java class at school and were doing very early on stuff. We are given a few methods and the knowledge of how if else statements, while loops, etc work. We use a program called greenfoot. The objective of the project is to have the character go around and pick up all the leaves, then place them at the end of the row and repeat. The order is changed so you need control statements. I am encountering an issue where at the end of each row, I will place a leaf, then pick it up and loop that forever. I have tried to solve it with variables to no avail. My code is here:
public void rowSweep() {
boolean turnCheck = false;
boolean leafCheck = true;
if (foundLeaf() && (leafCheck)) {
pickLeaf();
leafCheck = true;
}
else if (canMove() && (!facingNorth())) {
walk();
leafCheck = true;
}
else if (hasLeaf()) {
while (hasLeaf()) {
placeLeaf();
leafCheck = false;
}
}
else {
turnLeft();
while (canMove() && (!facingNorth())) {
walk();
turnCheck = true;
}
if (!canMove() && (turnCheck)) {
turnLeft();
walk();
turnLeft();
}
}
}
There are no syntax errors, just it doesn't do it properly. How can I make it so that I can move on after I place it instead of infinitely repeating?
Related
I am writing a program in JAVA where I need to change a boolean, but I am not able to fix it.
The lay out is as follows
while(statement){
Boolean behind = true;
if (behind == true){
do something
behind = false;
}
if (behind == false){
do something else
behind = true;
}
}
So basically my program needs to iterate 'doing something' and 'doing something else'. But I reckon my boolean behind is not changed by the if-statement, since that 'version' of behind only lives within the statement. Any suggestions on how to cope with this?
Do not use var == true/false. This may reduce performance and makes the code unclear. Use var instead of var == true and !var instead of var == false.
Use an else statement instead of checking the condition's opposite.
if (behind) {
//...
behind = false;
} else {
//...
behind = true;
}
3. **Define the boolean outside `while`.**
This also solves your problem because you don't "re-check" the variable.
Boolean behind = true;
while(statement){
if (behind){
do something;
behind = false;
}else{
do something else;
behind = true;
}
}
Define the boolean before the while block.
Boolean behind = true;
while(statement){
if (behind){
do something;
behind = false;
} else {
do something;
behind = true;
}
}
To summarize I am making a program for a metro ticket system. and I am using set and get methods for it, when it comes to boolean values (since I need to validate that the person enters enough money for the ticket) how am i supposed to put in the main class( it is defined in brain) using the set method and an if statement.Here is a little fraction of the entire code and the rest is on github(https://github.com/alexxei4/subwayticket). The main is basically the class that will be used for interaction with the user and the brain is where alot of the actions are defined.All help is appreciated, please and thank you.
if (Choice1a == 10){
if(subway1.ticketcounter1(true);){
System.out.println("PRINT SUCCESSFUL, COLLECT YOUR TICKET!");
}
if(subway1.ticketcounter1(false);){
System.out.println("INSEFFICIENT FUNDS, PLEASE ADD MORE");
}
This is not how you evaluate boolean values, you just place the value in an if statement and it will proceed if true and refuse if false, also there is no need to duplicate the statement when you can just place an else block to handle situations that are not true:
if(subway1.ticketcounter1) {
System.out.println("PRINT SUCCESSFUL, COLLECT YOUR TICKET!");
}
else {
System.out.println("INSEFFICIENT FUNDS, PLEASE ADD MORE");
}
Also do not include semicolons in if statements, that's incorrect syntax. Read more about how to use use boolean values here: https://codingbat.com/doc/java-if-boolean-logic.html
EDIT:
After reading through your Github code I see that ticketcounter1 indeed is a method, but what it's doing is trying to change the value of ticketcounter1 like it's a referenced object, but boolean are primitive data types and can't be referenced, and even if they could it still wouldn't work because Java is a pass-by-value language. Read here for more information on that.
public void ticketcounter1(boolean ticketcounter1){
if (credit1 > total1){
ticketcounter1 = true;
}
else {
ticketcounter1 = false;
}
}
public void ticketcounter2(boolean ticketcounter2){
if (credit2 > total2){
ticketcounter2 = true;
}
else {
ticketcounter2= false;
}
Like the other answer said you should be returning the value as boolean instead of trying to change it:
public boolean ticketcounter1(){
if (credit1 > total1){
return true;
}
else {
return false;
}
}
public boolean ticketcounter2(){
if (credit2 > total2){
return true;
}
else {
return false;
}
}
But all in all your code demonstrated fundamental flaws in understanding how the language works, I would suggest picking up a good Java for beginners kind of book or do some introductory online tutorials. Here is a good place to start your learning journey: https://docs.oracle.com/javase/tutorial/java/index.html
You code is like this
public void ticketcounter1(boolean ticketcounter1){
if (credit1 > total1){
ticketcounter1 = true;
}
else {
ticketcounter1 = false;
}
}
public void ticketcounter2(boolean ticketcounter2) {
if (credit2 > total2){
ticketcounter2 = true;
}
else {
ticketcounter2= false;
}
}
It should be like this. Instead of using the variable and passing it though parameter. Use getter. Besides that your code won't run since subway1.ticketcounter1(true) is giving nothing. It is only changing variables stored in Brain.java. No information is being sent to main.
public boolean ticketcounter1(){
if (credit1 > total1){
return true;
}
else {
return false;
}
}
public boolean ticketcounter2(){
if (credit2 > total2){
return true;
}
else {
return false;
}
}
You can create functions without parameters. I don't know what were you trying to do?
if (Choice1a == 10){
if(subway1.ticketcounter1()){
System.out.println("PRINT SUCCESSFUL, COLLECT YOUR TICKET!");
}
if(subway1.ticketcounter1()){
System.out.println("INSEFFICIENT FUNDS, PLEASE ADD MORE");
}
}
subway1.ticketcounter1() will give either true and false. Do not use ; in if statement condition. ; ends the statement. Check this guide to learn about use of semi-colon If you do want to use ; The code should look like this
if (Choice1a == 10){
boolean ticketCounter1 = subway1.ticketcounter1();
if(ticketCounter1){
System.out.println("PRINT SUCCESSFUL, COLLECT YOUR TICKET!");
} else {
System.out.println("INSEFFICIENT FUNDS, PLEASE ADD MORE");
}
}
P.S You don't need two ifs if-else would be better in this case
if(condition) {
// Conditions is true
} else {
// Condition is false
}
I have this code
spinRoullete.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if (errors()){
something
return;}
if (!errors()){
something else}
And this is for errors
private boolean errors() {
if (Rone.isChecked()) {
if (nr1.getText().length() == 0) {
nr1.setError("");
} else {
nr1.setError(null);
}
} if (Rtwo.isChecked()) {
if (nr1.getText().length() == 0) {
nr1.setError("");
} else {
nr1.setError(null);
}
if (nr2.getText().length() == 0) {
nr2.setError("");
} else {
nr2.setError(null);
}
}
Something here it's wrong and I don't know what .. The texterrors appears, and disappear when I complete the nr1, or nr2 (edittexts) but something it's wrong with the second if from onClick. When the errors disappear I want to go forward to that second if ( that with something else).. What should I edit to do this?
First off, minor optimization improvement: You have this code (formatted for improved readability, same code):
if (errors()){
something...
return;
}
if (!errors()){
something else...
}
But you don't need that least one since you have a return statement:
if(errors()){
something
return;
}
something else...
The method is called once instead of twice if there isn't an error, so you avoid problems there.
But you never return any visible value from errors(). Most likely, you have return true at the bottom, meaning it always goes into the first if statement. Simply change the method:
private boolean errors() {
boolean i1 = false;//if no errors, return false
if (Rone.isChecked()) {
if (nr1.getText().length() == 0) {
nr1.setError("");
i1 = true;//There is at least one error
} else {
nr1.setError(null);
}
}
if (Rtwo.isChecked()) {
if (nr1.getText().length() == 0) {
nr1.setError("");
i1 = true;//there is at least one error
} else {
nr1.setError(null);
}
if (nr2.getText().length() == 0) {
nr2.setError("");
return true;//This is the last thing that can happen, so just return true. There is at least one error, this one
} else {
nr2.setError(null);
return i1;//there could have been an error earlier, so return i1
}
}
return i1;//and if the last box isn't checked, return i1 here
}
Most likely, you have return true at the bottom of the method. That means it will always go into the first if-statement and return even if there are no errors.
And you should really start looking into indentation conventions, some of the code you posted is very hard to read because of that
I created a while loop which i want to stop when it becomes true
so i put:
while(!vending1.cansEmpty()) {
vending1.clickCan();
count++;
}
now it has been set so that the vending machine has 10 cans inside
and every time you call the method clickCan() it minus's 1 can,
but the while loop doesn't end when it the machine is empty (method becomes true), it just goes on infinitly
I am not sure why though
public class VendingMachine(){
private Integer cans;
public VendingMachine(int numCans) {
this.cans = numCans
}
public void clickCan() {
cans--;
}
public boolean cansEmpty() {
if (cans <= 0) {
return true;
} else {
return false;
}
}
}
I think you just need to make sure that your cans empty function returns a boolean.
I have a function when has an if-else statement. It essentially looks like this:
if(boolean == true)
{
// do something
boolean = false;
}
else if(boolean == false)
{
// do the other thing
boolean = true;
}
Now, my understanding is that the if statement will exit and return control to the function and then continue according to the changed boolean value. But I'm clearly missing something because my code is not exiting the original 'if'/'else if' statement (whichever the original case). Can anyone tell me what I've missed?
Well as requested, additional data about the code is that it is a part of my android project and each condition in the if-else block has a nested function and the boolean(global) value is being set/unset withing these functions. So the code now looks like this:
dummyFunction(){
boolean = checkIfTrueOrFalse();
if (boolean) {
onClick( public void onClick(){
// do something
boolean = false;}
} else if(boolean == false){
onClick( public void onClick(){
// do something
boolean = true;}
}
}
Any ideas?
if(boolean == true)
{
// do something
boolean = false;
}
if (boolean == false)
{
// do the other thing
boolean = true;
}
When you do this, then the program will flow to the second condition. In an if/else if statement, if the if statement has been satisfied, then the program will ignore the else if block.
Your current code simply flows through the first if block and then skips the else if statement to end the block.
void someMethod()
{
boolean aBoolean = true;
if(aBoolean == true)
{
// do something
aBoolean = false;
}
else if(aBoolean == false)
{
// do the other thing
aBoolean = true;
}
}
When someMethod will execute, since aBoolean is assigned with true, control will come to if block cause the condition becomes true. if it was false, then the control will come to else part.
We have many good answers/comments already but just wanted to add something here -
1.
if (condition) {
} else {
}
is a single code construct. The condition will be evaluated at the beginning at run time and java will decide which block to execute i.e. the if block or the else block. Only 1 of the 2 can be executed.
Java allows us to nest if/else. That means we can have something like below -
if(condition1){
} else if (condition2) {
} else if (condition3) {
} else {
}
It is effectively same as below -
if (condition1) {
} else {
if (condition2) {
} else {
if (condition 3) {
} else {
}
}
}
Here, it should be noted that only the block which satisfies the condition will be executed. If none of the conditions is met, then the inner most else will be executed (i.e. the else block of condition3 )
Finally, I feel that your confusion is between the below blocks
boolean aBoolean = true;
if(aBoolean == true)
{
// do something
aBoolean = false;
} else if(aBoolean == false)
{
// do the other thing
aBoolean = true;
}
VS
boolean aBoolean = true;
if(aBoolean == true)
{
// do something
aBoolean = false;
}
if(aBoolean == false)
{
// do the other thing
aBoolean = true;
}
In the latter of the 2 examples, there are 2 independent if blocks and both will get executed (off course, this is not logically correct but it is a legal java code.)
Could you provide more info regarding your code not exiting either of the 2 blocks? Doing System.out.println() of variables within your blocks might be able to help you determine why your code is not exiting.
You could use an if/else pair instead of an if/else-if as the parameter that your code depends on is would be either true/false. If the if-block is not satisfied, automatically the else-block would be traversed.
Your code is actually a shortcut for
if (boolean) {
// do something
boolean = false;
} else {
if (!boolean) {
// do the other thing
boolean = true;
}
}
Written this way, it maybe becomes clearer that the inner if nested in the else case will not be processed if the first if condition was already met.
Well I've solved it (taking inputs from here of course). I just added a call to the function within the nested functions and it worked. Now the code looks like this:
public static void dummyFunction(){
boolean = checkIfTrueOrFalse();
if (boolean) {
onClick( public void onClick(){
// do something
dummyFunction();
boolean = false;}
} else if(boolean == false){
onClick( public void onClick(){
// do something
dummyFunction();
boolean = true;}
}
}