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If-else One line statement (with string and integer) [closed]

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I'm creating a program. This code below is the Java program. Checking if the value of B and H, input by the user is equal to zero. If it is true, then a math formula will execute which is p = b*h then if it is false, a string will be shown on the console. But the thing is, it keeps on giving me an error that string cannot be converted to int or int cannot be converted to string.
Here is the code:
import java.util.Scanner;
public class StaticProject{
static {
Scanner input = new Scanner (System.in);
int B = input.nextInt();
int H = input.nextInt();
int P;
int solution = B>=0 && H>=0 ? P = B*H : "java.lang.Exception: Breadth and height must be positive";
}
How can I improve my coding when it comes in doing this oneline bi-conditionals statement? Any tips?

your solution variable Type is int, and your else statement returns an String, this is the cause of error.
you can change your code to this:
Scanner input = new Scanner (System.in);
int B = input.nextInt();
int H = input.nextInt();
int P;
if (B >= 0 && H >= 0) {
P = B*H;
} else {
throw new Exception("Breadth and height must be positive");
}
System.out.println(P);
}

You are trying to assign string to an int variable, if your statement is evaluated as false.
You need to use if/else condition, which both sides have the same type.
In your case, it's not possible.
another possibility is use System.out.println() command, to print the result of whatever resulted by the condition.

There is no virtue in writing code in as few lines as possible. By all means, don't write unnecessary code, but just don't think that concise code is objectively "better".
The best type of code to write is simple code. Maybe it's a little more verbose; but if you write code that people can understand at a glance, they know what it does straight away.
Here is how I would write it:
if (B < 0 || H < 0) {
// Actually, non-negative, rather than positive.
throw new Exception("Breadth and height must be positive");
// Or, maybe, don't even use exceptions at all:
// System.out.println("The message");
// return;
}
// No need for `solution` variable.
P = B * H;
System.out.println(P);
Of course, you might argue this isn't code everybody will understand at a glance. Sure. Readability is subjective; but I assert that anybody with just a little bit of experience in Java can work it out.
You can write a conditional ?: expression which results in an exception being thrown in the case of the condition being false.
// Define a method which does the throwing.
static int justThrow(String message) throws Exception {
throw new Exception(message);
}
// In the main method:
int solution = B>=0 && H>=0 ? P = B*H : justThrow("Breadth and height must be positive");
I emphasize that you can, but you shouldn't do this. It's obscure. It's trying to be "a bit too clever". It will have people reading your code and scratching their heads, because they will wonder why you wrote a method for something so simple; what is the solution variable for, given that it will have the same value as P etc.

OutofBounds Exception [closed]

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I am trying here to measure how many white spaces there are in text typed in a JTextArea. I am getting an outofbounds exception. Why so?
Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 0
at java.lang.String.charAt(String.java:658)
at ClassTest.main(ClassTest.java:11)
import javax.swing.*;
public class ClassTest {
public static void main(String [] args) {
JFrame frame = new JFrame();
JTextArea textarea = new JTextArea();
frame.setSize(300, 300);
frame.add(textarea);
frame.setVisible(true);
String text=textarea.getText();
int count = 0;
for(int i=0;i>=text.length();i++) {
char spacecount = text.charAt(i);
if(spacecount==' ') {
System.out.print(count++);
}
}
}
}

I believe it should be < not >= for the 'for' loop condition.
Your for loop is as follows:
for(int i=0; i>=test.length();i++){
char spacecount = test.charAt(i);
if(spacecount==' '){
System.out.println(count++);
}
}
Let us take a walk through the for loop. The first part says, we create an int called i and initialize it to 0;
i = 0;
Next part says, keep looping while this condition is true. So it will loop while
i >= test.length()
The next part says, after each iteration, let us add 1 to i. The only reason it could possibly run is
if test.length() == 0;
if test.length() == 1;
0 is not >= 1 so it won't run. That means, the only reason it could run is if the length is 0. Now if the string is of length 0, it would be "".
What is the charAt(0)? Nothing. There is no 0 index. If the String were "a". Then charAt(0) would return "a". It is reaching for something that does not exist and therefore will not run. So one of the problems is that you need to change the condition to < instead of >=. Next, it is recommended to use camel case for fields (such as spacecount) which means you should change it to spaceCount.
Lastly, it may not occur in this case but let us say, test = null. What happens? What is null.length()? Is that even possible? Well actually it will compile in the case that test = null; and then test.length() is executed. However, you cannot call such a method on a null value so you will get the dreaded runtime error, the "NullPointerException". This says, uh oh. We have a string that points to null. Well we cannot do anything with it. Here comes the exception. So in future code, it is recommended to be able to account for such cases. So what do we do? How do we check if a String == null? Well... String == null. So in the future, if it is possible for something to be null, put the for loop in an if statement that says:
if(test != null){
//put for loop here
} else{
//do something else
}

Single equal in different situation [closed]

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I have this code...
class Test {
public static void main(String[] args) {
Boolean mySuperBoolean = Boolean.FALSE;
System.out.print("a");
if (mySuperBoolean = Boolean.TRUE) {
System.out.print("b");
}
System.out.print("c");
}
}
I am new to Java, but I knew single equal (=) is used to assign. And double equals (==) is used to check if object is referred to the same location in memory. However, in this case I do not understand how the 'b' is being printed with a single equals, but I understand changing it to a double equals sign will not print it out

if (mySuperBoolean = Boolean.TRUE) will assign Boolean.TRUE to your mySuperBoolean variable and the condition will evaluate to true, hence whatever is inside your if it will always execute

The result of the assignment operator = will be the assigned value. So if (mySuperBoolean = Boolean.TRUE) will always evaluate to true.

Assignment is an expression which resolves to whatever was assigned, in this case(mySuperBoolean = Boolean.TRUE) is an expression which resolves to Boolean.TRUE.
This is really only useful in a few specific situations. One such case is the following idiom:
String line;
while ((line = readLine()) != null) {
//...
}
Or even
i = j = k = 0; // equal to: i = (j = (k = 0))
It's a controversial feature because it allows probable bugs such as yours to compile successfully. To mitigate this, some people will invert the operands (a "yoda condition"):
if (Boolean.TRUE == mySuperBoolean)
This works because if I forget the second equals then the compiler will throw an error because Boolean.TRUE is final and cannot be assigned to.

In essence, what happens here boils down to:
if (Boolean.TRUE) {
System.out.print("b");
}
That assignment puts TRUE into the variable, the variable is boolean, and checked for its current value, end of story.

Can I return Boolean value in a loop statement? [closed]

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I just came up with a problem returning a Boolean value in accordance with a given condition. I thought in order to check the given condition for full possibilities I need to use for loop. But when I tried to compile it, it gives me error, possibly because there is uncertainty returning a Boolean value using for loop. Here is an original problem:
Return true if the given string contains a "bob" string, but where the middle 'o' char can be any char.
bobThere("abcbob") → true
bobThere("b9b") → true
bobThere("bac") → false
And here is my code:
public boolean bobThere(String str)
{
for(int i=0; i<str.length()-3; i++)
{
if (str.length()>=4): && str.charAt(i)=='b' && str.charAt(i+2)=='b')
{
return true;
}
else
return false;
else if (str.length()==4 && str.charAt(0)=='b' && str.charAt(2)=='b')
{
return true;
}
else
{
return false;
}
}
}
I just wanted to ask :
1. Can I fix the this code for returning a value. I mean, can I use for loop and return specific value for a given condition? If yes, please could you give me a sample.
2. Or are there any ways other than for loop to solve this problem.
Thanks in advance.

The compiler error is almost certainly because you have an elseif after an else. That's invalid.
Looking at your code, what you seem to want to do is loop through the string, and then return true if you're at the start of a b?b string. I'm not sure why you have your second if condition in there - at the moment your code would check the first and third characters of the string on every iteration of the loop, if the string happens to be exactly four characters long. Pointless, it doesn't need to be there. The check for length isn't necessary at all.
Additionally, your end condition for the loop is currently i < string.length()-3. This means that the final three characters of the string will not be checked. You would need to change this to either i <= string.length()-3 or i < string.length()-2 to solve this.
Your else return false stuff is going to give you a serious problem. Your code will enter the loop once, and then either return true or false, without ever going to the next phase of the loop. What you should do is loop through the string, and if you find what you're looking for, return true. Otherwise, don't return at all, and keep going with the loop. If you get to the end of the loop it means you never found what you were looking for, so you can at that point return false.
Taking those comments into account, your revised code would look like this (please note I haven't compiled or run this):
public boolean bobThere(String str)
{
for(int i = 0; i <= str.length() - 3; i++)
{
if (str.charAt(i) == 'b' && str.charAt(i + 2) == 'b')
{
return true;
}
}
return false;
}

Error when check an empty element in array [closed]

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why cannot I check if a place in array is empty ?
I got this wrong message:
The operator == is undefined for the argument type(s) int, null"
on the marked line
private static int findNr(int[] trans)
{
int emptyPlace=0;
for (int i=0; i<trans.Length -1;i++)
{
--> if( trans[i] = null) <--
return emptyPlace = trans[i];
}
return emptyPlace;
}

You can not compare primitive data type for null. int is primitive data type.

You have to do
if( trans[i] == null)
instead of
if( trans[i] = null)
^-----------Mistake
Anyway in which language you have written the code?

You try to assign null to the array element at position i
To check if the element is null you have to do:
if(trans[i] == null)
{
...
}
but this expression doesn't make any sense since an int can never be null (unless its a nullable int (int?)) so the condition will always be false

Primitive cannot be checked with the null. So for particular primitive types use their default value to check.
i.e for int default value is 0 and for
double default value is 0.0 etc.
So check as:
if(intr[i]==0){
//some logic
}

if( trans[i] = null)
In the above line your are using assignment operator = in place of comparison operator ==. If condition expects the final value after computation to be of the type boolean. Hence you get the error.
Also your trans[i] is an primitive int value which cannot be compared to a null. (Only objects can be null in java)
The assignment operator = will only work in case of boolean variables, something like this:
boolean flag = false;
if(flag=true) {
// this condition will be true
}

First, you mispelled the == comparison. Should be:
if (trans[i] == null)
Second, the above doesn't works. Primitive values can never be null, when you declare any int variable, it's 0 by default.
Thats why:
int[] v = new int[3];
for (int i = 0; i < v.length; i++)
System.out.println(v[i]);
Outputs this:
0
0
0
You should either work with Integer objects array or review your logic.

1- You have forgot '=' ---> if (trans[i] == null)
2- You can't compare primitive value (int) with null