Java Vector indexOf()
indexOf() Java Vector类方法用于获取指定元素首次出现的索引在向量中。 Java indexOf()方法有两种不同类型,可以根据其参数加以区分。这些是:
Java Vector indexOf(Object o)方法
Java Vector indexOf(Object o,int index)方法
indexOf(Object o)方法:
此方法用于获取向量中指定元素首次出现的索引。如果找不到该元素,则返回-1。
indexOf(Object o,int index> c)方法:
此方法用于获取向量中指定元素首次出现的索引。它开始从指定的索引开始向前搜索元素。如果找不到该元素,则返回-1。
语法
以下是
indexOf()方法的声明:
public int indexOf(Object obj)
public int indexOf(Object obj, int index)
参数
参数 |
说明 |
必需/可选 |
index |
这是一个索引,从此处开始向前搜索元素。 |
必需 |
obj |
它是要搜索的元素。 |
必需 |
返回
indexOf()方法返回此向量中第一次出现的指定元素的索引,或者返回-1如果向量不包含元素。
异常
IndexOutOfBoundsException -如果数组的索引为该方法,则抛出异常超出范围,即(index <0 || index> size())。
兼容版本
Java 1.2及更高版本
示例1
import java.util.*;
public class VectorIndexOfExample1 {
public static void main(String arg[]) {
//Create an empty Vector
Vector < Integer > in = new Vector < > ();
//Add elements in the vector
in.add(100);
in.add(200);
in.add(300);
in.add(400);
//Obtain an index of first occurrence of the specified element
System.out.println("Index of element is: " +in.indexOf(300));
}
}
输出:
示例2
import java.util.*;
public class VectorIndexOfExample2 {
public static void main(String arg[]) {
//Create a first empty vector
Vector<String> vec = new Vector<>(4);
//Add elements in the first vector
vec.add("Java");
vec.add("JavaScript");
vec.add("Android");
vec.add("Python");
//Obtain an index of first occurrence of the specified element
System.out.println("Index of element is: " +vec.indexOf("C"));
System.out.println("The element is not found.");
}
}
输出:
Index of element is: -1
The element is not found.
示例3
import java.util.*;
public class VectorIndexOfExample3 {
public static void main(String arg[]) {
//Create a first empty vector
Vector<String> vec = new Vector<>(4);
//Add elements in the first vector
vec.add("Facebook");
vec.add("Whatsapp");
vec.add("Twitter");
vec.add("Instagram");
vec.add("Skype");
//this would start searching of element from index -2
System.out.println("Index of element is found at: " +vec.indexOf("Skype", -2));
}
}
输出:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -2
at java.base/java.util.Vector.indexOf(Vector.java:430)
at myPackage.VectorIndexOfExample3.main(VectorIndexOfExample3.java:14)
示例4
import java.util.*;
public class VectorIndexOfExample4 {
public static void main(String arg[]) {
//Create an empty Vector
Vector < Integer > in = new Vector < > ();
//Add elements in the vector
in.add(101);
in.add(201);
in.add(301);
in.add(401);
in.add(501);
//this would start searching of element from index 2
System.out.println("Index of element is found at: " +in.indexOf(401, 2));
}
}
输出:
Index of element is found at: 3