Java中的 Arraylist.contains()

Java中的 ArrayList contains() 方法用于检查指定元素是否存在于给定列表中。

句法：

public boolean contains(Object)
object-element to be searched for

参数：
object- 要测试其在此列表中的存在的元素

回报：
如果在列表中找到指定的元素，则返回 true，否则返回 false。

代码#1：以整数形式演示 contains() 方法的工作原理

// Java code to demonstrate the working of
// contains() method in ArrayList
  
// for ArrayList functions
import java.util.ArrayList;
  
class GFG {
    public static void main(String[] args)
    {
  
        // creating an Empty Integer ArrayList
        ArrayList arr = new ArrayList(4);
  
        // using add() to initialize values
        // [1, 2, 3, 4]
        arr.add(1);
        arr.add(2);
        arr.add(3);
        arr.add(4);
  
        // use contains() to check if the element
        // 2 exits or not
        boolean ans = arr.contains(2);
  
        if (ans)
            System.out.println("The list contains 2");
        else
            System.out.println("The list does not contains 2");
  
        // use contains() to check if the element
        // 5 exits or not
        ans = arr.contains(5);
  
        if (ans)
            System.out.println("The list contains 5");
        else
            System.out.println("The list does not contains 5");
    }
}

输出：

The list contains 2
The list does not contains 5

代码#2：演示字符串contains() 方法的工作原理

// Java code to demonstrate the working of
// contains() method in ArrayList of string
  
// for ArrayList functions
import java.util.ArrayList;
  
class GFG {
    public static void main(String[] args)
    {
  
        // creating an Empty String ArrayList
        ArrayList arr = new ArrayList(4);
  
        // using add() to initialize values
        // ["geeks", "for", "geeks"]
        arr.add("geeks");
        arr.add("for");
        arr.add("geeks");
  
        // use contains() to check if the element
        // "geeks" exits or not
        boolean ans = arr.contains("geeks");
  
        if (ans)
            System.out.println("The list contains geeks");
        else
            System.out.println("The list does not contains geeks");
  
        // use contains() to check if the element
        // "coding" exits or not
        ans = arr.contains("coding");
  
        if (ans)
            System.out.println("The list contains coding");
        else
            System.out.println("The list does not contains coding");
    }
}

输出：

The list contains geeks
The list does not contains coding

实际应用：
在搜索操作中，我们可以检查给定元素是否存在于列表中。

参考：
甲骨文文档