Boolean Arrays true/false switch

[LetsG0Blue]

I'm totally lost. I'm suppose to have make an Boolean Array which displays false originally and then alternate between true & false;

For example:
arr[0] = true;
arr[1] = false;
arr[2] = true;

Then I'm suppose to print in void printBoolean(boolean[] arr)

Can somebody veer me in the right direction?

public class Boolean {

	void fillBoolean(boolean[] arr) {
		// fillBoolean will fill the arr array passed in with alternating true false values.
		
		 boolean[] trueFalse = new boolean[] {true};
		 
		 int n, i = n*2;
		
		 for (n = 0; i < trueFalse.length; n++) {
			 trueFalse[i] = !trueFalse[i];
			}
		 
	}
	void printBoolean(boolean[] arr){
		
		// The printBoolean routine will print out the contents of the array arr passed in.
		
		int index;
		
		for (index = 0; index + 1 <= 20; index++)
            System.out.println(fillBoolean(arr)[index]); 
    }
		
	public static void main(String[] args) {

	}

}

[SJF]

1. Don't initialize your array in fillBoolean, the array is passed by the caller.
2. That's not how arrays are initialized ... Arrays (The Java™ Tutorials > Learning the Java Language > Language Basics)
3. That link will also address why System.out.println(fillBoolean(arr)[index]); -> System.out.println(arr[index]));
4. I assume the array should be initialized in main then printed? then passed to fillBoolean, then (re-)printed ... if so void -> static void on both of your functions.
5. The class name Boolean is bad... Boolean already exists in java, and is kinda important.

[jim829]

2. That's not how arrays are initialized ... Arrays (The Java™ Tutorials > Learning the Java Language > Language Basics).

Really?

boolean arr[] = new boolean[3];
arr[0] = true;
arr[1] = false;
arr[2] = true;

// or

int[] intArray = new int[]{1,2,3,4,5,6,7,8,9,10};
boolean [] boolArray = new boolean[] {true, false, true, false};

Works for me.

Regards,
Jim

[SJF]

Yeah, ok, so you might do that... if no. DON'T DO THAT.

boolean[] trueFalse = new boolean[] {true};

is a one member array.

not really useful and trueFalse[ANYTHING BUT 0] = no good.

boolean[] trueFalse = new boolean[] {false,false,false,false,false,false,false,false,f alse,false,false,false,false};

could work... but really?

[SJF]

But anyway Primitive Data Types (The Java™ Tutorials > Learning the Java Language > Language Basics) default boolean = false,

so

   boolean[] bool = new boolean[400];  // is a new 400 element false array.

[jim829]

I'm not certain of the point you are making. He initialized his array to true.

Regards,
Jim

[jim829]

The issue was not whether he was initializing to all false values or whether it was a 1 x1 array. Or whether his/her code is optimal. This issue was whether s/he could initialize that way. You said no. I said yes.

Regards,
Jim

[SJF]

.... make an Boolean Array which displays false originally ....

Was all I was addressing.

[LetsG0Blue]

How do I get the value to appear? I.E. the output

arr[0] = true
arr[1] = false
arr[2] = true

public class Boolean {

	void fillBoolean(boolean[] arr) {
		// fillBoolean will fill the arr array passed in with alternating true false values.
		 
		 int n = 1, i = n*2;
		
		 for (i = 1; i < arr.length; i++) {
			 arr[i] = !arr[i];
			}
		 
	}
	void printBoolean(boolean[] arr){
		
		// The printBoolean routine will print out the contents of the array arr passed in.
		
		int index;
		
		for (index = 0; index + 1 <= 20; index++)
            System.out.println(arr[index]); 
    }
		
	public static void main(String[] args) {

	}

}

[SJF]

Well, your printBoolean() should do the trick. Create your array in the main function and call printBoolean(yourArray) (You'll have to declare printBoolean static first.)

[LetsG0Blue]

I'm still real new at this and haven't had much time to practice. How would I go about calling my printBoolean?

public class Boolean {

	void fillBoolean(boolean[] arr) {
		// fillBoolean will fill the arr array passed in with alternating true false values.
		 
		 int n = 1, i = n*2;
		
		 for (n = 1; i < arr.length; n++) {
			 arr[i] = !arr[i];
			}
		 
	}
	static void printBoolean(boolean[] arr) {
		
		// The printBoolean routine will print out the contents of the array arr passed in.
		
		int index;
		
		for (index = 0; index + 1 <= 20; index++)
            System.out.println(arr[index]);
			System.out.println(arr);
    }
		
	public static void main(String[] args) {
 
		boolean[] arr = new boolean[] {true};
			     
			

	}

[SJF]

    printBoolean(arr);

[LetsG0Blue]

I'm getting this error.

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
at Boolean.printBoolean(Boolean.java:21)
at Boolean.main(Boolean.java:28)

true

it has something to do with

	static void printBoolean(boolean[] arr) {
		
		// The printBoolean routine will print out the contents of the array arr passed in.
		
		int index;
		
		for (index = 0; index + 1 <= 20; index++)
            System.out.println(arr[index]);
    }

public class Boolean {

	void fillBoolean(boolean[] arr) {
		// fillBoolean will fill the arr array passed in with alternating true false values.
		 
		 int n = 1, i = n*2;
		
		 for (n = 1; i < arr.length; n++) {
			 arr[i] = !arr[i];
			}
		 
	}
	static void printBoolean(boolean[] arr) {
		
		// The printBoolean routine will print out the contents of the array arr passed in.
		
		int index;
		
		for (index = 0; index + 1 <= 20; index++)
            System.out.println(arr[index]);
    }
		
	public static void main(String[] args) {
 
		boolean[] arr = new boolean[] {true};
		
			printBoolean(arr);
			

	}
}

[SJF]

Your for loop in printBoolean is looking for a boolean array of length 20. instead of (index = 0; index + 1 <= 20 ..... -> (index = 0; index < arr.length; index++) just like the for loop in fillBoolean.
Speaking of which .. (n=1; i < arr.length; n++) I don't think that's what you want... (but the i < arr.length is probably right, just not the n business)

[LetsG0Blue]

Your for loop in printBoolean is looking for a boolean array of length 20. instead of (index = 0; index + 1 <= 20 ..... -> (index = 0; index < arr.length; index++) just like the for loop in fillBoolean.
Speaking of which .. (n=1; i < arr.length; n++) I don't think that's what you want... (but the i < arr.length is probably right, just not the n business)

I don't believe it's right either, but I need every other array to print out true..

Example:

true
false
true
false

[SJF]

If you get your OOB Exception to go away. (i < array.length is your friend). Your printBoolean will work.

Now then: when boolean (primitives) are initialized they are false by default. Enter fillBoolean(). So... every other entry should be false... a[i] = !a[i-1] ? Maybe? Note: array[-1] will also get you an OOB Exception.

[LetsG0Blue]

If you get your OOB Exception to go away. (i < array.length is your friend). Your printBoolean will work.

Now then: when boolean (primitives) are initialized they are false by default. Enter fillBoolean(). So... every other entry should be false... a[i] = !a[i-1] ? Maybe? Note: array[-1] will also get you an OOB Exception.

Doesn't work still returns just false ten times... wish my professor actually went over this material during his lectures.

[Mickeycricky]

I've got to do this same problem. It's very confusing.

[SJF]

Look: There are two ways to get what you want. (Well more than that, but here are two)

First:
1. Set first item in array to true -> arr[0] = true;
2. Use a for loop (from 1 to 9) and set each array item to NOT it's predecessor -> arr[i] = !arr[i-1]

Second:
1. Go through the loop from 0 to 9 and set each even item true (they are false to begin with). if( i % 2 == 0)

.... or go through loop from 0 to 8 ; i+=2 setting arr[i] to true....

But steps in main are
A. initialize array.
B. call fillBoolean(yourArray)
C. call printBoolean(yourArray)

[tamilarasi]

check your for loop

   for (index = 0; index + 1 <= 20; index++)
            System.out.println(arr[index]);
    }

this got issue.

Refer this link:ttp://stackoverflow.com/questions/4958235/why-does-arrayindexoutofboundsexception-occur-and-how-to-avoid-it-in-android

Finally you put correct value for array index range