java Java 中的 CopyOnWriteArrayList indexOf()方法

Java 中的 CopyOnWriteArrayList indexOf()方法

原文:https://www . geeksforgeeks . org/copy onwriterarraylist-indexof-method-in-Java/

The indexOf(Object o) method of CopyOnWriteArrayList returns the first occurrence of the element passed in the list. It returns -1 if the element is not present in the list.

语法:

java public int indexOf(Object o)

参数:该函数接受一个参数 o ，该参数的第一次出现将被返回。

返回值:函数返回元素的第一次出现。如果该元素不在列表中，则返回-1。

以下程序说明了上述功能:

程序 1:

```java // Java Program to illustrate the CopyOnWriteArrayList // indexOf() method in Java import java.util.concurrent.CopyOnWriteArrayList; import java.util.*;

public class GFG {     public static void main(String[] args)     {

// create object of CopyOnWriteArrayList         CopyOnWriteArrayList ArrLis             = new CopyOnWriteArrayList();

// Add elements         ArrLis.add(32);         ArrLis.add(67);         ArrLis.add(67);         ArrLis.add(100);

// print CopyOnWriteArrayList         System.out.println("CopyOnWriteArrayList: " + ArrLis);

// first occurrence of 67         System.out.println("indexOf value: " + ArrLis.indexOf(67));     } } ```

Output:

```java CopyOnWriteArrayList: [32, 67, 67, 100] indexOf value: 1

```

程序 2:

```java // Java Program to illustrate the CopyOnWriteArrayList // indexOf() method in Java import java.util.concurrent.CopyOnWriteArrayList; import java.util.*;

public class GFG {     public static void main(String[] args)     {

// create object of CopyOnWriteArrayList         CopyOnWriteArrayList ArrLis             = new CopyOnWriteArrayList();

// Add elements         ArrLis.add(32);         ArrLis.add(67);         ArrLis.add(67);         ArrLis.add(100);

// print CopyOnWriteArrayList         System.out.println("CopyOnWriteArrayList: "                                          + ArrLis);

// 200 is not present         System.out.println("indexOf value: "                          + ArrLis.indexOf(200));     } } ```

Output:

```java CopyOnWriteArrayList: [32, 67, 67, 100] indexOf value: -1

```
The indexOf(E e, int index) method of CopyOnWriteArrayList returns the first occurrence of the element passed in the list after position index. It returns -1 if the element is not present in the list.

语法:

java public int indexOf(E e, int index)

参数:该函数接受两个参数，如下所述:
- 索引:指定从中搜索事件的索引。
- e :指定从位置索引第一次出现要返回的元素。
返回值:函数返回位置索引后元素的第一次出现。如果该元素不在列表中，则返回-1。

异常:如果指定的指数为负，该函数将抛出指数。

以下程序说明了上述功能:

程序 1:

```java // Java Program to illustrate the CopyOnWriteArrayList // indexOf() method in Java import java.util.concurrent.CopyOnWriteArrayList; import java.util.*;

public class GFG {     public static void main(String[] args)     {

// create object of CopyOnWriteArrayList         CopyOnWriteArrayList ArrLis             = new CopyOnWriteArrayList();

// Add elements         ArrLis.add(32);         ArrLis.add(67);         ArrLis.add(67);         ArrLis.add(67);

// print CopyOnWriteArrayList         System.out.println("CopyOnWriteArrayList: "                                            + ArrLis);

// first occurrence of 67 from 2nd index         System.out.println("indexOf value: "                           + ArrLis.indexOf(67, 2));     } } ```

Output:

```java CopyOnWriteArrayList: [32, 67, 67, 67] indexOf value: 2

```

程序 2:

```java // Java Program to illustrate the CopyOnWriteArrayList // indexOf() method in Java import java.util.concurrent.CopyOnWriteArrayList; import java.util.*;

public class GFG {     public static void main(String[] args)     {

// create object of CopyOnWriteArrayList         CopyOnWriteArrayList ArrLis             = new CopyOnWriteArrayList();

// Add elements         ArrLis.add(32);         ArrLis.add(67);         ArrLis.add(67);         ArrLis.add(100);

// print CopyOnWriteArrayList         System.out.println("CopyOnWriteArrayList: "                                          + ArrLis);

// -1 is out of range, hence exception         System.out.println("indexOf value: "                       + ArrLis.indexOf(-1, 200));     } } ```

输出:

java Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1 at java.util.concurrent.CopyOnWriteArrayList.indexOf(CopyOnWriteArrayList.java:198) at java.util.concurrent.CopyOnWriteArrayList.indexOf(CopyOnWriteArrayList.java:263) at GFG.main(GFG.java:24)