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Java - Deque contains(Object) Method
The Java Deque contains(Object) returns true if this deque contains the specified element. In case of custom objects, equals() methd should be implemented so that contains can compare objects correctly.
Declaration
Following is the declaration for java.util.Deque.contains() method
public boolean contains(Object o)
Parameters
o − The object to be checked as contained in deque.
Return Value
This method returns true if this deque contains the specified element, else false.
Exception
ClassCastException − if the class of the specified element is incompatible with this deque (optional)
NullPointerException − if the specified element is null and this deque does not permit null elements (optional)
Example 1
The following example shows the usage of Java Deque contains() method. We're using Integers. We'll be adding few elements and then checking if certain element is present or not.
package com.tutorialspoint; import java.util.ArrayDeque; import java.util.Deque; public class DequeDemo { public static void main(String[] args) { // create an empty deque Deque<Integer> deque = new ArrayDeque<>(); // use add() method to add elements in the deque deque.add(20); deque.add(30); deque.add(10); deque.add(18); // let us print all the elements available in deque System.out.println("Deque = " + deque); // deque contains element 10 if (deque.contains(10)) { System.out.println("element 10 is present in the deque"); } else { System.out.println("element 10 is not present in the deque"); } // deque does not contain element 25 if (deque.contains(25)) { System.out.println("element 25 is present in the deque"); } else { System.out.println("element 25 is not present in the deque"); } } }
Output
Let us compile and run the above program, this will produce the following result −
Deque = [20, 30, 10, 18] element 10 is present in the deque element 25 is not present in the deque
Example 2
The following example shows the usage of Java Deque contains() method with Strings. We'll be adding few elements and then checking if certain element is present or not.
package com.tutorialspoint; import java.util.ArrayDeque; import java.util.Deque; public class DequeDemo { public static void main(String[] args) { // create an empty deque Deque<String> deque = new ArrayDeque<>(); // use add() method to add elements in the deque deque.add("Welcome"); deque.add("to"); deque.add("tutorialspoint"); deque.add(".com"); // let us print all the elements available in deque System.out.println("Deque = " + deque); // deque contains element tutorialspoint if (deque.contains("tutorialspoint")) { System.out.println("element tutorialspoint is present in the deque"); } else { System.out.println("element tutorialspoint is not present in the deque"); } // deque does not contain element html if (deque.contains("html")) { System.out.println("element html is present in the deque"); } else { System.out.println("element html is not present in the deque"); } } }
Output
Let us compile and run the above program, this will produce the following result −
Deque = [Welcome, to, tutorialspoint, .com] element tutorialspoint is present in the deque element html is not present in the deque
Example 3
The following example shows the usage of Java Deque contains() method with Student objects. We'll be adding few elements and then checking if certain element is present or not.
package com.tutorialspoint; import java.util.ArrayDeque; import java.util.Deque; public class DequeDemo { public static void main(String[] args) { // create an empty array deque Deque<Student> deque = new ArrayDeque<>(); // use add() method to add elements in the deque deque.add(new Student(1, "Julie")); deque.add(new Student(2, "Robert")); deque.add(new Student(3, "Adam")); // let us print all the elements available in deque System.out.println("Deque = " + deque); // deque contains element Robert if (deque.contains(new Student(2, "Robert"))) { System.out.println("Student Robert is present in the deque"); } else { System.out.println("Student Robert is not present in the deque"); } // deque does not contain element Jane if (deque.contains(new Student(4, "Jane"))) { System.out.println("Student Jane is present in the deque"); } else { System.out.println("Student Jane is not present in the deque"); } } } class Student { int rollNo; String name; Student(int rollNo, String name){ this.rollNo = rollNo; this.name = name; } @Override public String toString() { return "[ " + this.rollNo + ", " + this.name + " ]"; } @Override public boolean equals(Object obj) { Student s = (Student)obj; return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name); } }
Output
Let us compile and run the above program, this will produce the following result −
Deque = [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]] Student Robert is present in the deque Student Jane is not present in the deque
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