Predicate and BiPredicate in Java

Understanding boolean-valued functions in Java

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Introduction

In Mathematics, a predicate is a boolean-valued function that returns 1or 0, i.e., true or false. Java leveraged the mathematical concept of the predicate and introduced the Predicate interface in Java 8.

A Boolean-valued function is a function of the type f : X → B, where X is an arbitrary set and where B is a Boolean domain, whose elements are interpreted as logical values, for example, 0 = false and 1 = true.
— Wikipedia

Predicate

Predicate is a functional interface in Java that accepts exactly one input and can return a boolean value. Before going into it, we first need to understand the Functional Interface.

Functional Interface

A functional interface is an interface that contains exactly one abstract method. It is also called Single Abstract Method (SAM) Interfaces. In Java, an interface is made functional by annotating it with @FunctionalInterface.

We know that predicate accepts an input and returns a boolean value. But where is it used? The predicate can be used wherever a boolean output is expected—Eg. Stream’s filter method.

Example

Let's create the Employee class with the fields id , name , age , gender , and role .

Now we want to filter the employees based on the below use cases.

• Employees who are Male and age greater than 25
• Employees who are Female and are Managers.

We will create two predicates for the above use cases.

We can pass the above predicates to the filter() method to filter the employees based on the predicate's result.

Output

Male and age greater than 25
Id: 2, Name: Steve Rogers, Age: 28, Gender: MALE, Role: MANAGER
Female and Manager
Id: 3, Name: Natasha Romanoff, Age: 23, Gender: FEMALE, Role: MANAGER

Predicate Composition

Multiple predicates can be composed together to form a chain of predicates. The composition is done with built-in methods. and(), or() , negate() and isEqual() .

and()

Returns true only if all the predicates return, else false. It is equivalent to logical AND.

or()

Returns true if any of the predicates return, else false. It is equivalent to logical OR.

negate()

Returns true if the predicate returns false and vice versa. It is equivalent to logical NOT.

isEqual()

Returns a predicate that checks if two values are equal. The equality is decided usingObject.equals() method.

Output

and() operation
true
false
or() operation
true
true
negate() operation
false
isEqual() operation
true

BiPredicate

BiPredicate is a functional interface in Java that accepts two inputs and can return a boolean value. It is similar to the Predicate interface. The only difference is that it takes two inputs instead of one.

Output

10 divisible by 2: true
5 divisible by 3: false
8 divisible by 4: true

Conclusion

• Predicate is a functional interface in Java that accepts a single input and can return a boolean value.
• BiPredicate is a functional interface in Java that accepts two inputs and can return a boolean value.
• Predicate and BiPredicate are usually used to apply in a filter for a collection of objects.

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