In mathematics Predicates are functions that can be either True or False. In JAVA8 Predicates are functional interfaces with only functional method test.
As Predicate is defined as a functional interface in JAVA8 it can be used as the assignment target for a lambda expression or method reference.
we can do boolean operations such as and, or, not(negate) with different instances of Predicate. These default methods are –
| Default Method Name | Explanation |
|---|---|
| and() | It does logical AND of the predicate on which it is called with another predicate. Example: predicate1.and(predicate2) |
| or() | It does logical OR of the predicate on which it is called with another predicate. Example: predicate1.or(predicate2) |
| negate() | It does boolean negation of the predicate on which it is invoked. Example: predicate1.negate() |
Following code uses JAVA8 predicate and replaceIf method, now available in collections, to check from the list of transaction to get only those transaction that has a value more than 2lakh and are done online.
public class UnderstandingRemoveIf {
static Predicate<Transaction> checkTransactionAmount = new Predicate<Transaction>() {
@Override
public boolean test(Transaction transaction) {
return Math.round(transaction.amount) < 200000;
}
};
static Predicate<Transaction> isTransactionOnline = new Predicate<Transaction>() {
@Override
public boolean test(Transaction transaction) {
return transaction.transactionMethod!='O';
}
};
public static void main(String[] args) {
List<Transaction> transactions = new ArrayList<>();
Transaction transaction1=new Transaction(10000.8d, 'C');
Transaction transaction2=new Transaction(150000d, 'O');
Transaction transaction3=new Transaction(300000d, 'O');
transactions.add(transaction1);
transactions.add(transaction2);
transactions.add(transaction3);
// Get all transactions that are done online of more then 2 lakh
transactions.removeIf(checkTransactionAmount.or(isTransactionOnline));
System.out.println(transactions);
}
}
class Transaction{
double amount;
char transactionMethod; // O for online
public Transaction(double amount,char transactionMethod) {
this.amount=amount;
this.transactionMethod=transactionMethod;
}
@Override
public String toString() {
return amount+","+transactionMethod;
}
}