集合包含 Java 中的()方法，示例
原文:https://www . geesforgeks . org/collection-contains-in-method-in-Java-with-examples/
java.util.Collection 接口的包含(Object element) 用于检查该集合中是否存在元素‘element’。此方法返回一个描述元素存在的布尔值。如果元素存在，则返回 true，否则返回 false。
语法:
Collection.contains(Object element)
参数:该方法接受一个强制参数元素，类型为对象，将在该集合中进行检查。
返回值:这个方法返回一个布尔值，描述元素的存在。如果添加了元素，它将返回 true，否则将返回 false。
异常:此方法抛出以下异常:
- ClasscasteException: If the class of the specified element prevents it from being added to this collection.
- [T0】 NullPointerException: 【T1] If the specified element is empty and this collection does not allow empty elements.
以下示例说明了 Collection contains()方法:
示例 1: 使用链接列表类
// Java code to illustrate boolean contains() method
import java.io.*;
import java.util.*;
public class GFG {
public static void main(String args[])
{
// creating an empty LinkedList
Collection<String> list = new LinkedList<String>();
// use add() method to add elements in the list
list.add("Geeks");
list.add("for");
list.add("Geeks");
// Output the present list
System.out.println("The list is: " + list);
// Checking the presence of Geeks
// using contains() method
boolean result = list.contains("Geeks");
// printing the result
System.out.println("Is Geeks present in the List: "
+ result);
}
}
输出:
The list is: [Geeks, for, Geeks]
Is Geeks present in the List: true
例 2: 使用 ArrayDeque 类
// Java code to illustrate contains() method
import java.util.*;
public class ArrayDequeDemo {
public static void main(String args[])
{
// Creating an empty ArrayDeque
Collection<String> de_que = new ArrayDeque<String>();
// Use add() method to add elements into the Deque
de_que.add("Welcome");
de_que.add("To");
de_que.add("Geeks");
de_que.add("4");
de_que.add("Geeks");
// Displaying the ArrayDeque
System.out.println("ArrayDeque: " + de_que);
// Checking the presence of Geeks
// using contains() method
boolean result = de_que.contains("Geeks");
// printing the result
System.out.println("Is Geeks present in the ArrayDeque: "
+ result);
}
}
输出:
ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
Is Geeks present in the ArrayDeque: true
示例 3: 使用数组列表类
// Java code to illustrate contains() method
import java.io.*;
import java.util.*;
public class ArrayListDemo {
public static void main(String[] args)
{
// create an empty array list with an initial capacity
Collection<Integer> arrlist = new ArrayList<Integer>(5);
// use add() method to add elements in the list
arrlist.add(15);
arrlist.add(20);
arrlist.add(25);
// Output the present list
System.out.println("ArrayList: " + arrlist);
// Checking the presence of 20
// using contains() method
boolean result = arrlist.contains(20);
// printing the result
System.out.println("Is 20 present in the ArrayList: "
+ result);
}
}
输出:
ArrayList: [15, 20, 25]
Is 20 present in the ArrayList: true
示例 4: 演示空指针异常
// Java code to illustrate boolean contains()
import java.util.*;
public class LinkedListDemo {
public static void main(String args[])
{
// Creating an empty ArrayList
Collection<String>
list = new ArrayList<String>();
// Displaying the list
System.out.println("The ArrayList is: " + list);
try {
// Checking presence of null
list.contains(null);
}
catch (Exception e) {
System.out.println("Exception: " + e);
}
}
}
输出:
The ArrayList is: []
版权属于：月萌API www.moonapi.com，转载请注明出处
