November 24, 2018

Create a simple counter in java 11, using java IntSupplier – Then test it using IntStream – a functional programming way.

We will create a simple counter in java.

  1. It will have a default initialization of 0.
  2. It will have a constructor, which can be used to set the seed value of this counter.
  3. It will implement Iterator interface
  4. It will implement IntSupplier interface
package com.refactored.util;

import java.util.Iterator;
import java.util.function.IntSupplier;

public class Counter implements Iterator<Integer>, IntSupplier {

    private int count = 0;

    public Counter(){}

    public Counter(int seed) {
        count =  seed;
    }

    @Override
    public Integer next() {
        return ++count;
    }

    @Override
    public boolean hasNext(){
        return  count < Integer.MAX_VALUE;
    }

    @Override
    public int getAsInt() {
        return next().intValue();
    }
}


private int count = 0; this is our variable which stores the count. And it is initialized with 0.

public Counter(){} this is our default constructor.

This is the second constructor, which initializes the counter with the given value.

public Counter(int seed) {
  count =  seed;
}

Now, We are going to create a class to use this counter with it’s default value.

package com.refactored.util;

import java.util.function.IntPredicate;
import java.util.stream.IntStream;

public class UseCounter {
    public static void main(String[] args) {
        Counter counter = new Counter();

        //Print the 10 elements
        IntPredicate limit_10 = limitStream(10);

        IntStream.generate(counter)
                .takeWhile(limit_10)
                .forEach(System.out::println);
    }

    private static IntPredicate limitStream(int lastCount) {
        return (int value) -> (value <= lastCount);
    }
}

After running this, we get the following output.

1
2
3
4
5
6
7
8
9
10

Now, we will create a counter with seed value of 100, and print from 101 to 110.

Modified portion of code looks like this.

int seed = 100;
Counter counter = new Counter(seed);

//Print the 10 elements
IntPredicate limit_10 = limitStream(seed+10);

Let us, run this.

101
102
103
104
105
106
107
108
109
110

So, We have successfully created a counter. 🙂

Happy coding.

 

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