How find if arraylist contains a value which is in class field?

Question

I have class:

static class AnotherClass {
        int number;
        String isPrime;

        public int getNumber() {
            return number;
        }

        public String getPrime() {
            return isPrime;
        }

        public void setNumber(int number) {
            this.number = number;
        }

        public void setPrime(String prime) {
            isPrime = prime;
        }

    }

and in main class i have:

    List<AnotherClass> listx = new ArrayList<AnotherClass>();//just a arraylist

for (int z = 0; z < howManyQuestions; z++) {//in loop i add class with fields
            AnotherClass classx = new AnotherClass();
            int valuex = Integer.parseInt(keyboardkey.readLine());

            classx.setNumber(valuex);//save value in this class

            String answer = Check(valuex);//i just get here string answer YES NO
            classx.setPrime(answer);

            listx.add(classx);//and i add this two fields of class to list

            System.out.println();

        }

INPUT: (i add value and check if it was input before)
3
4
3

OUTPUT
NO
NO
YES

How can i check if, for example value "3" is containing by list?

Use a for loop and call the appropriate getXXX method. That's it. — Hovercraft Full Of Eels, Jul 10 '11 at 19:01

score 2 · Accepted Answer · answered Jul 10 '11 at 19:02

2

1 AnotherClass must implement equals() (and implement hashCode() accordingly).

2 Use method contains(Object o) from listx.

answered Jul 10 '11 at 19:02

SJuan76

24,532
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score 2 · Answer 2 · answered Jul 10 '11 at 19:07

2

private boolean contains(int i)
{
    for(int j: listx.getNumber()) { if(i == j) return true; }
    return false;
}

answered Jul 10 '11 at 19:07

Eng.Fouad

115,165
71
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score 1 · Answer 3 · answered Jul 10 '11 at 19:02

A Few notes -

your class doesn't require static. That has a use if you're declaring an inner class.

You have a container class holding a string that's dependant on an int, as well as the int. It'd be more idiomatic to have the check inside your class, e.g.

class AnotherClass {
        int number;


        public int getNumber() {
            return number;
        }

        public String getPrime() {
            return check(number)
        }

       private boolean check() { ... whatever logic you had .. }
}

If you're looking for "contains" functionality, you'd probably use a HashSet, or a LinkedHashSet( if you want to preserve the ordering ). If you want to do this with your created class you'll need to implement a hashCode() method to tell the hashSet how to know if it has a duplicate value.

Or you can just iterate over your list.

score 1 · Answer 4 · answered Jul 10 '11 at 19:04

You have to implement equals() for AnotherClass. The default equals() compares identity instead of value equality.

The javadoc for List.contains() says:

Returns true if this list contains the specified element. More formally, returns true if and only if this list contains at least one element e such that (o==null ? e==null : o.equals(e)).

How find if arraylist contains a value which is in class field?

4 Answers4