I am working through the JavaBat questions and am confused about my logic.
Here's the task:
Given a day of the week encoded as 0=Sun, 1=Mon, 2=Tue, ...6=Sat, and
a boolean indicating if we are on vacation, return a string of the
form "7:00" indicating when the alarm clock should ring. Weekdays, the
alarm should be "7:00" and on the weekend it should be "10:00". Unless
we are on vacation -- then on weekdays it should be "10:00" and
weekends it should be "off".
alarmClock(1, false) → "7:00" alarmClock(5, false) → "7:00"
alarmClock(0, false) → "10:00"
Here's my code:
public String alarmClock(int day, boolean vacation) {
if ( (day >=1 && day <=5) && (!vacation)) {
return "7:00";
} else if ( (day >=1 && day <=5) && (vacation)) {
return "10:00";
} else {
return "off";
}
}
Why do these two tests fail?
alarmClock(0, false) → "10:00" "off" X
alarmClock(6, false) → "10:00" "off" X
Surely, this line covers it?
if (day >=1 && day <=5) && (!vacation))
how about this?
public String alarmClock(int day, boolean vacation) {
if (day >=1 && day <=5) {
return vacation ? "10:00" : "7:00";
} else {
return vacation ? "off" : "10:00";
}
}
Note it does depend if your coding convention allows the use of the turnary operator. But in this case I think the logic is easier to read.
Surely, this line covers it?
if ((day >=1 && day <=5) && (!vacation))
No, that line doesn't cover it. If the day is Sunday or Saturday (0 or 6), the first part of your "and" expression (day >=1 && day <=5) will be false, since 0 and 6 are not between 1 and 5 inclusive.
The only branch that handles days 0 and 6 is your else branch: "off".
This is a great time to use helper methods to express your logic closer to the English description:
if ( isWeekday(day) ) {
if ( vacation ) {
//what to return here?
} else {
//what to return here?
}
} else {
if ( vacation ) {
//what to return here?
} else {
//what to return here?
}
}
Then you just need to implement isWeekday:
private boolean isWeekday(int day) {
return /*fill this in*/;
}
Although the ternary operator is useful here, as this problem can be done in a single return statement, the following code below allows readability.
public String alarmClock(int day, boolean vacation) {
if(vacation){ //if we are on vacation
if(day > 0 && day < 6){ //if it is weekday and we are on vacation
return "10:00";
}
else return "off"; //it must be the weekend!
}
//from here on out all the cases where vacation is true have been weeded out
if(day > 0 && day < 6){
return "7:00";
}
else return "10:00";
}
if ((day == 0 || day == 6) && (!vacation) || (day >= 1 && day <= 5) && (vacation)) {
return "10:00";
}
if ((day >= 1 && day <= 5) && (!vacation)) {
return "7:00";
}
return "off";
public String alarmClock(int day, boolean vacation) {
if (((day==0)||(day==6))&&(!vacation)){
return "10:00";
}
else if (((day!=0)||(day!=6))&&(!vacation)){
return "7:00";
}
else if (((day==0)||(day==6))&&(vacation)){
return "off";
}
else{
return "10:00";
}
}
Related
i would like to print leap years in between two years given in a format like
'[2120,2024,2028]'.i want them with these commas and square brackets..kindly help me with this.in java
my program:
System.out.print("[");
for(int i=2017;i<=2040;i++)
{
if(i%4==0)
{
System.out.print(i);
if(i!=2040)
{
System.out.print(",");
}
}
}
System.out.print("]");
if i change the value the comma is not working right
It is easier to put a comma before each number and not after. The effect is the same, but then you just need to make the first leap year a special case:
System.out.print("[");
boolean isFirstLeapYear = true;
for (int i=2017;i<=2040;i++) {
if (i%4 == 0 && (i%100 != 0 || i%400 == 0)) {
if (isFirstLeapYear) {
isFirstLeapYear = false;
} else {
System.out.print(",");
}
System.out.print(i);
}
}
System.out.print("]");
There is more rules about leap year.
I suggest you to study this method and use it in your code:
boolean isLeapYear(year) {
if (year % 400 == 0) {
return true;
} else {
if ((year % 4 == 0) && (year % 100 != 0)) {
return true;
} else {
return false;
}
}
}
I started learning java on my own a few weeks back and I keep running up to the same basic problem, where I can't call a method from another method in the same class. I either get a "symbol not found" error (I think because the method is out scope or the method just doesn't work anymore. The following code is part of a java exercise for creating a calender sort of a programme. I'll use the // in code commentaries to indicate, where exactly is the problem.
public class MyDate {
private int year;
private int month;
private int day;
private static String[] strMonths = {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
private static String[] strDays = {"Sunday", "Monday", "Tuesday",
"Wednesday", "Thursday", "Friday", "Saturday"};
private static int[] daysInMonths = {31, 28, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
public static boolean isLeapYear(int year) { // This is the first method, which works fine
// when being called from the main method.
if (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0)) {
return true;
} else {
return false;
}
};
public static boolean isLeapYear; // I put this declaration in, because I got
// "symbol not found" errors, when referencing the method from the second method.
// I'm guessing it partially invalidates the first declaration.
public static boolean isValidDate(int year, int month, int day) { // The second method
if ((year >= 1 ) && (year <= 9999)){
if ((month >= 0) && (month <= 11)) {
if ((day >= 1) && ((month == 0) || (month == 2) || (month == 4) || (month == 6)
|| (month == 7) || (month == 9) || (month == 11)) && (day <= 31)) {
return true;
}
else if ((day >= 1) && ((month == 3) || (month == 5) || (month == 8)
|| (month == 10) && (day <= 30))) {
return true;
}
else if (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0)){
// Code from the first method (above), which I would like to replace with just a reference
// to the first method (for instance (isLeapYear = true)),
// but it doesn't work the same as the code above (or at all).
if ((month == 1) && (day == 29)) {
return true;
}
else
if ((day >= 1) && ((month == 1) && (day <= 28))) {
return true;
}
else {
return false;
}
}
}
}
return isValidDate; }
For reference, the method isLeapYear works as it's supposed to, when testing it with this main method:
public static void main(String[] args) {
System.out.println(isLeapYear(1900)); // false
System.out.println(isLeapYear(2000)); // true
System.out.println(isLeapYear(2011)); // false
System.out.println(isLeapYear(2012)); // true
}
}
Thanks for your help!
Remove public static boolean isLeapYear; from your code and every time you need to call a function, in this case public static boolean isLeapYear(int year) { ..} you must use a parenthesis to let the compiler know that you are actually calling a function there.
In this case you should go with isLeapYear(year)
and then if (isLeapYear(year)) { .. } else {..}
Given package name of MyApplication (substitute your package name in each place this one occurs below) import isLeapYear as shown below.
package MyApplication;
public class MyDate {
public static boolean isLeapYear(int year) { // This is the first method, which works fine
// when being called from the main method.
if (((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0)) {
return true;
} else {
return false;
}
};
}
Main class:
package MyApplication;
import static MyApplication.MyDate.isLeapYear;
public class NewClass{
public static void main(String[] args) throws Exception
{
System.out.println(isLeapYear(1900)); // false
System.out.println(isLeapYear(2000)); // true
System.out.println(isLeapYear(2011)); // false
System.out.println(isLeapYear(2012));
}
}
public class CodingBat {
public static void main(String[] args){
CodingBat object = new CodingBat();
System.out.print(object.parrotTrouble(true,20));
}
public boolean parrotTrouble(boolean talking, int hour) {
if(talking == false){
return false;
}
else if(hour > 7 || hour >20){
return true;
}
}
}
I am confused, why I am getting an error where the public method parrotTrouble is underlined saying it must return a boolean, which I currently have?
Compiler says you need to return some value since your method return type is boolean.
You have returned false in If condition, and return true in else if condition.
you need to return something outside of if/else if as well.
something as below, as per comments from #Andreas, code can be reduced to below
Original as per OP
public boolean parrotTrouble(boolean talking, int hour) {
if (talking == false) {
return false;
} else if (hour > 7 || hour > 20) {
return true;
}
return booleanValue; // can be true/false as per your logic
}
Edit
public boolean parrotTrouble(boolean talking, int hour) {
return (talking && (hour > 7 || hour > 20));
}
As pointed by #Codebender, wither use if else condition, then no
need to return boolean value at the last, but if you are using if -
else if you have to return boolean value at the last. As compiler is
also not sure that it will go in one of the conditions surely.
public boolean parrotTrouble(boolean talking, int hour) {
boolean answer = false;
if(talking == false){
answer = false;
}
else if(hour < 7 || hour >20){
answer = true;
}
return answer;
}
Thank you for your help, I changed my code to this and it worked correctly and answered the question <3
I am learning java but stuck with this issue, I am writing a simple code but this error is throwing up again
Can some one help me with what wrong i am doing?
public String alarmClock(int day, boolean vacation) {
if (day >= 1 && day <= 5) {
if (vacation = true) {
return "10:00";
}
else (vacation = false) {return "7:00";}
}
else {
if (vacation = true) {
return "off";
}
else (vacation = false) {return "10:00";}
}
}
the error which it is giving is-
Error: else (vacation = false) {return "7:00";}
^
Syntax error, insert "AssignmentOperator ArrayInitializer" to complete ArrayInitializerAssignement
What the output i want is this -
alarmClock(1, false) → "7:00"
alarmClock(5, false) → "7:00"
alarmClock(0, false) → "10:00"
I know this may be simple but i am just new to java so i want to learn this.
Thanks in advance !
In a condition use == (comparison), not = (assignment) :
change
if (vacation = true)
to
if (vacation == true)
or even better
if (vacation)
Beside that, else (vacation = false) is invalid syntax, and you don't need it anyway. Just write else.
if (day >= 1 && day <= 5) {
if (vacation) {
return "10:00";
} else {
return "7:00";
}
} else {
if (vacation) {
return "off";
} else {
return "10:00";
}
}
I am having trouble nesting these if statements from Python to Java.
def leapyear(yearr):
if (year % 4 == 0):
if (year % 100 == 0):
if (year % 400 == 0):
return True
else:
return False
else:
return True
else:
return False
I currently am working to convert the above to Java:
boolean leapyear(int year) {
if (year % 4==0) {
if (yearr%100==0) {
if (year%400==0) {
else
return false;
}
else
return true;
}
else
return false;
}
}
However, my Java conversion is giving me errors, mainly because I do not think my nested conditionals have the right closed braces. Can you give me any hints or resources that can help me figure this out?
It's not good practice to have so many possible exit points. Also, if you don't want to reinvent the wheel, you can use Java library code, for example:
boolean isLeapYear(int year){
GregorianCalendar cal = new GregorianCalendar();
return cal.isLeapYear(year);
}
Your else statements need braces too, you forgot a return statement for the innermost if, and you misspelled yearr in one location:
boolean leapyear(int year) {
if (year % 4==0) {
if (year % 100 == 0) {
if (year % 400 == 0) {
return true;
} else {
return false;
}
} else {
return true;
}
} else {
return false;
}
}
Java doesn't need the indentation like Python does, but it'd help make your branching structure more readable if you did use it anyway:
boolean leapyear(int year) {
if (year % 4 == 0) {
if (year % 100 == 0) {
if (year % 400 == 0) {
return true;
} else {
return false;
}
} else {
return true;
}
} else {
return false;
}
}
You don't need as many return statements here, the year % 400 == 0 already evaluates to a boolean:
boolean leapyear(int year) {
if (year % 4 == 0) {
if (year % 100 == 0) {
return year % 400 == 0;
} else {
return true;
}
} else {
return false;
}
}
or as a one-liner:
boolean leapyear(int year) {
return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
}
For completeness sake, here is the Python version the way I would write it:
def leapyear(year):
return year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)
or better still, use calendar.isleap() instead.
What about removing the ifs altogether?
public boolean leapyear(int year) {
return (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
}
heres my attempt:
boolean leapyear(int year)
{
if (year % 4 == 0)
{
if (year % 100 == 0)
{
return (year % 400 == 0);
}
else
{
return true
}
}
return false;
}
or use this:
return Java.util.GregorianCalendar.getInstance().isLeapYear(year)
boolean leapyear(int year)
{
if (year % 4==0)
{
if (year%100==0)
{
if (year%400==0)
{
return true;
}
else
{
return true;
}
}
else``
{
return false;
}
}
}