LinkedBlockingQueue contains() method in Java

The contains(Object obj) method of LinkedBlockingQueue returns true if queue contains the object obj passed as parameter. It returns true, if and only if, this queue contains at least one element e which is equal to object o passed as parameter i.e. e.equals(o). This method is very helpful to check whether the queue has an element or not.

Syntax:

public boolean contains(Object o)

Parameter: This method takes a mandatory parameter o which is the object to be check in the queue.

Return Value: This method returns true if this queue contains the object passed as parameter. Else it returns false.

Below programs illustrate contains() method of LinkedBlockingQueue class:

Program 1: Check whether a queue of numbers contains a number n or not. Number n is passed as input to contains() of LinkedBlockingQueue.

// Java Program Demonstrate contains(Object o)
// method of LinkedBlockingQueue

import java.util.concurrent.LinkedBlockingQueue;

public class GFG {

    public static void main(String[] args)
    {
        // define capacity of LinkedBlockingQueue
        int capacityOfQueue = 50;

        // create object of LinkedBlockingQueue
        LinkedBlockingQueue<Integer> linkedQueue
            = new LinkedBlockingQueue<Integer>(capacityOfQueue);

        // Add element to LinkedBlockingQueue
        linkedQueue.add(2300);
        linkedQueue.add(1322);
        linkedQueue.add(8945);
        linkedQueue.add(6512);

        // print LinkedQueue
        System.out.println("linkedQueue: " + linkedQueue);

        // check whether LinkedBlockingQueue contains 6512
        boolean response1 = linkedQueue.contains(6512);

        // print result
        System.out.println("LinkedBlockingQueue contains "
                           + "number 6512 : "
                           + response1);

        // check whether LinkedBlockingQueue contains 5324
        boolean response2 = linkedQueue.contains(5324);

        // print result
        System.out.println("LinkedBlockingQueue contains"
                           + " number 5324 : "
                           + response2);
    }
}

Output:

linkedQueue: [2300, 1322, 8945, 6512]

LinkedBlockingQueue contains number 6512 : true
LinkedBlockingQueue contains number 5324 : false

Program 2: Check whether a queue of Employees contains certain employee e or not. Details of employee e are passed as input to contains() of LinkedBlockingQueue.

// Java Program Demonstrate contains(Object o)
// method of LinkedBlockingQueue.

import java.util.concurrent.LinkedBlockingQueue;

public class GFG {

    // create an Employee Object with
    // position and salary as an attribute
    public class Employee {

        public String name;
        public String position;
        public String salary;

        Employee(String name, String position, String salary)
        {
            this.name = name;
            this.position = position;
            this.salary = salary;
        }

        @Override
        public String toString()
        {
            return "Employee [name=" + name + ", position="
                + position + ", salary=" + salary + "]";
        }
    }

    // Main Method
    public static void main(String[] args)
    {
        GFG gfg = new GFG();
        gfg.containsMethodExample();
    }

    public void containsMethodExample()
    {

        // define capacity of LinkedBlockingQueue
        int capacity = 50;

        // create object of LinkedBlockingQueue
        LinkedBlockingQueue<Employee> linkedQueue
            = new LinkedBlockingQueue<Employee>(capacity);

        Employee emp1 = new Employee("Aman",
                                     "Analyst",
                                     "24000");
        Employee emp2 = new Employee("Sachin",
                                     "Developer",
                                     "39000");

        // Add Employee Objects to linkedQueue
        linkedQueue.add(emp1);
        linkedQueue.add(emp2);

        // print LinkedQueue
        System.out.println("linkedQueue: " + linkedQueue);

        // Employee to be checked
        Employee checkEmp1 = new Employee("Sanjeev",
                                          "Tester",
                                          "26000");

        // check whether linkedQueue contains emp1
        boolean response1 = linkedQueue.contains(emp1);

        // print results
        System.out.println("linkedQueue contains "
                           + emp1.toString() + " : "
                           + response1);

        // check whether linkedQueue contains checkEmp1
        boolean response2 = linkedQueue.contains(checkEmp1);

        // print results
        System.out.println("linkedQueue contains "
                           + checkEmp1.toString() + " : "
                           + response2);
    }
}

Output:

linkedQueue: 
[Employee [name=Aman, position=Analyst, salary=24000], 
Employee [name=Sachin, position=Developer, salary=39000]]

linkedQueue contains Employee [name=Aman, position=Analyst, salary=24000] : true
linkedQueue contains Employee [name=Sanjeev, position=Tester, salary=26000] : false

Reference:
https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/LinkedBlockingQueue.html#contains-java.lang.Object-