Use java's ArrayList.contains() function to determine whether the ArrayList contains elements

Use Java's ArrayList.contains() function to determine whether the ArrayList contains elements

In Java programming, ArrayList is a commonly used data structure that can store any type of object and can be dynamically expanded. Sometimes we need to determine whether an ArrayList contains a specific element. In this case, we can use the contains() function of the ArrayList class.

The ArrayList class is one of the commonly used collection classes in Java programming and is located under the java.util package. It provides many convenient methods, including adding, deleting and finding elements, etc. The contains() function is used to determine whether the ArrayList contains a specific element. The syntax of the contains() function is as follows:

boolean contains(Object element)

Among them, element represents the element to be judged. The contains() function returns a Boolean value. If the element is contained in the ArrayList, it returns true; otherwise it returns false.

The following is an example code that uses the ArrayList.contains() function to determine whether the ArrayList contains elements:

import java.util.ArrayList;

public class ArrayListContainsExample {

public static void main(String[] args) {
    // 创建一个ArrayList
    ArrayList<String> list = new ArrayList<>();

    // 向ArrayList中添加元素
    list.add("apple");
    list.add("banana");
    list.add("orange");

    // 判断ArrayList是否包含某个元素
    System.out.println("ArrayList是否包含apple：" + list.contains("apple"));
    System.out.println("ArrayList是否包含pear：" + list.contains("pear"));
}

}

Run the above code, you can get the following output:

Whether the ArrayList contains apple: true
Whether the ArrayList contains pear: false

From It can be seen from the output that the ArrayList.contains() function correctly determines whether the ArrayList contains the specified element. In the above example, we created an ArrayList object and added three string elements. Then, we use the contains() function to determine whether the ArrayList contains the two elements "apple" and "pear" respectively, and verify it by printing the output results.

It should be noted that the contains() function will use the equals() method of the element to compare whether the elements are equal. Therefore, when using the contains() function, make sure that the element class has correctly implemented the equals() method.

Summary: This article introduces the method of using Java's ArrayList.contains() function to determine whether an ArrayList contains elements, and provides corresponding code examples. In this way, we can easily determine whether an ArrayList contains a specific element, thus improving programming efficiency.

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