CODEWITHSUNDEEP
javaboolean-logic
Onedaynerd
Onedaynerd

Reputation: 49

How to incorporate a boolean in a method JAVA

I having a hard time getting the right output because i dont know how boolean exactly works inside a method. I have an arraylist and I'm check for any duplicates in the arraylist Here's my code

public void rentOneInstrument(List<Instrument> instrumentList){
        String a="";
        String b="";
        boolean found = false;
        for (int j = 0; j < instrumentList.size(); j++) {
                a ="";
                a = instrumentList.get(j).getName();

                for (int i = j+1; i < instrumentList.size(); i++) {
                    b = instrumentList.get(i).getName();
                    System.out.println("a" + a + " b" + b);
                    if(a.equals(b)){
                        found = true;
                    }else {
                        found = false;
                    }
                }
        }
        if (found) {
            System.out.println("duplicate");
        }else{
            System.out.println("no duplicate");
        }
    }

Here is my output

a Cymbals b Drums,..
a Cymbals b Cello,..
a Cymbals b Cymbals,..
a Drums b Cello,..
a Drums b Cymbals,..
a Cello b Cymbals

no duplicate // prints no duplicate when there is clearly a duplicate in the output. How can i correct this?

Edit.. Btw I just a want a single out put that prints whether it found a duplicate or not inside the loop

Upvotes: 0

Views: 189

Answers (4)

tipiwiny
tipiwiny

Reputation: 409

public void rentOneInstrument(List<Instrument> instrumentList){

    boolean found=false;
    List<String> listString=new ArrayList<String>();

    for (Instrument inst: instrumentList){
        if(listString.contains(inst.getName())){

            found=true;
        }
        else{
            listString.add(inst.getName());
        }


    }

  if (found) {
            System.out.println("duplicate");
        }else{
            System.out.println("no duplicate");
        }


}

Upvotes: 0

StackFlowed
StackFlowed

Reputation: 6816

Consider the following input : 

a,b,c,a,d

Now whit your code it would be false as d is not repeated. It would over right the value for a that is repeated. Also once a element is fond that it is replanted you don't need to go through the entire loop of all elements hence there is a break.

public void rentOneInstrument(List<Instrument> instrumentList){
        String a="";
        String b="";
        boolean found = false;
        for (int j = 0; j < instrumentList.size(); j++) {
                a ="";
                a = instrumentList.get(j).getName();
                if(found) { break; } // Changed line here 
                for (int i = j+1; i < instrumentList.size(); i++) {
                    b = instrumentList.get(i).getName();
                    System.out.println("temp1 " + a + " temp2 " + b);
                    if(a.equals(b)){
                        found = true;
                        break; // Changed line here 
                    }
                }
        }
        if (found) {
            System.out.println("duplicate");
        }else{
            System.out.println("no duplicate");
        }
    }

Another way of doing it without a break would be 

public void rentOneInstrument(List<Instrument> instrumentList){
        String a="";
        String b="";
        boolean found = false;
        for (int j = 0; j < instrumentList.size() && !found; j++) {
                a ="";
                a = instrumentList.get(j).getName();

                for (int i = j+1; i < instrumentList.size() && !found; i++) { // Changed for condition to look at the found variable too.
                    b = instrumentList.get(i).getName();
                    System.out.println("temp1 " + a + " temp2 " + b);
                    if(a.equals(b)){
                        found = true;
                    }
                }
        }
        if (found) {
            System.out.println("duplicate");
        }else{
            System.out.println("no duplicate");
        }
    }

A much better way of doing this would be using sets that doesn't contain duplicates.

public void rentOneInstrument(List<Instrument> instrumentList){
     Set< Instrument > instrumentSet = new HashSet< Instrument >(instrumentList);
     if(instrumentList.size()== instrumentSet.size()) {
          System.out.println("no duplicate");
     } else {
          System.out.println("duplicate");
     }
}

Upvotes: 1

Adil Shaikh
Adil Shaikh

Reputation: 44740

Let found be false by default. and just set it true if any duplicate is found.

 if(a.equals(b)){
      found = true;
 }else {
      // found = false;
      // don't do this otherwise it will override previous `found` value
 }

Upvotes: 1

Dragondraikk
Dragondraikk

Reputation: 1679

if(a.equals(b)){
  found = true
}else {
    found = false;
}

This is your problem. This way only the last iteration of your loop will be stored in found. Since you are initializing it as false you don't need to set it to that again here.

   for (int i = j+1; i < instrumentList.size(); i++) {
      b = instrumentList.get(i).getName();
      System.out.println("temp1 " + a + " temp2 " + b);
      if(a.equals(b)){
         found = true;
      }
   }

Alternatively, you can use a break statement when you have found a match to get out of the loop like so:

if(a.equals(b)){
  found = true;
  break;
}else {
    found = false;
}

This way, found will be true and no other iterations will be performed, continuing after the end of the loop instead.

Upvotes: 2

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