Java - Deque contains(Object) 方法

Java Deque contains(Object) 方法返回 true，如果此 deque 包含指定的元素。对于自定义对象，应实现 equals() 方法，以便 contains 可以正确比较对象。

声明

以下是 java.util.Deque.contains() 方法的声明

public boolean contains(Object o) 

参数

o − 要检查是否包含在 deque 中的对象。

返回值

如果此 deque 包含指定的元素，则此方法返回 true，否则返回 false。

异常

ClassCastException − 如果指定元素的类与此 deque 不兼容（可选）

NullPointerException − 如果指定元素为 null，并且此 deque 不允许 null 元素（可选）

示例 1

以下示例显示了 Java Deque contains() 方法的用法。我们使用的是 Integer。我们将添加一些元素，然后检查某些元素是否存在。

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");    
      }
   }
}           

输出

让我们编译并运行上面的程序，这将产生以下结果：

Deque = [20, 30, 10, 18]
element 10 is present in the deque
element 25 is not present in the deque

示例 2

以下示例显示了 Java Deque contains() 方法与字符串一起使用的用法。我们将添加一些元素，然后检查某些元素是否存在。

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");    
      }
   }
}           

输出

让我们编译并运行上面的程序，这将产生以下结果：

Deque = [Welcome, to, tutorialspoint, .com]
element tutorialspoint is present in the deque
element html is not present in the deque

示例 3

以下示例显示了 Java Deque contains() 方法与 Student 对象一起使用的用法。我们将添加一些元素，然后检查某些元素是否存在。

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);
   }
}

输出

让我们编译并运行上面的程序，这将产生以下结果：

Deque = [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]]
Student Robert is present in the deque
Student Jane is not present in the deque