The pair class in C++ Standard Library is used a lot. We can implement our own user-defined pair class in Java and its object can be used anywhere just like any other parameter.
Note :
This class is equivalent to pair<int,int> class in java. You can create your own template or classes for other data types.
Syntax For defining the pair class can be:
class pair{
int first,second;
// constructor for assigning values
pair(int first,int second){
this.first = first;
this.second = second;
}
// function which returns a
pair values(){
return new pair(first,second);
}
// printing the pair class
@Override
public String toString(){
return "("+first+","+second+")";
}
}
- We can now play around with this class and even create an array of pairs, similar to the vector<pair<int,int>> in C++.
Example:
Java
// Java program to create a pair class// and initialize an array of that// pair class objectpublic class pair_example { public static void main(String[] args) { pair[] arr = new pair[5]; for (int i = 0; i < 5; i++) { arr[i] = new pair(i + 1, i + 2); } // printing an array of pairs easily for (pair i : arr) { System.out.println(i); } // to extract particular values int value = arr[3].second; System.out.println("Required Value = " + value); }}// user defined pair class of integer typeclass pair { int first, second; // constructor for assigning values pair(int first, int second) { this.first = first; this.second = second; } // function which returns a pair pair values() { return new pair(first, second); } // printing the pair class @Override public String toString() { return first + "," + second; }} |
Output
1,2 2,3 3,4 4,5 5,6 Required Value = 5
Implementation Example:
Suppose we need to store the ith prime number and its index together in a structure.
Java
// Java program to create a struct/pair class// for storing a prime number with its indexclass GFG { public static void main(String[] args) { // first N prime numbers int N = 30; // creating list of pairs java.util.ArrayList<pair> p = new java.util.ArrayList<>(); int index = 1; for (int i = 1; i <= N; i++) { if (isPrime(i)) { // creating new pair object and appending to // list p.add(new pair(index++, i)); } } System.out.println("i and the ith prime numbers are :"); System.out.println(p); } // function to check prime static boolean isPrime(int n) { if (n < 2) return false; for (int i = 2; i * i <= n; i++) { if (n % i == 0) return false; } return true; }}// user defined pair class of integer typeclass pair { int first, second; // constructor for assigning values pair(int first, int second) { this.first = first; this.second = second; } // function which returns a pair pair values() { return new pair(first, second); } // printing the pair class @Override public String toString() { return "(" + first + "," + second + ")"; }} |
Output
i and the ith prime numbers are : [(1,2), (2,3), (3,5), (4,7), (5,11), (6,13), (7,17), (8,19), (9,23), (10,29)]
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