Java字符串indexOf()

本文概述

• Java String indexOf()方法示例
• Java String indexOf（String substring）方法示例
• Java字符串indexOf（String substring, int fromIndex）方法示例
• Java字符串indexOf（int char, int fromIndex）方法示例

Java字符串indexOf()方法返回给定字符值或子字符串的索引。如果找不到, 则返回-1。索引计数器从零开始。

内部实施

public int indexOf(int ch) {
        return indexOf(ch, 0);
    }

签名

Java中有4种indexOf方法。下面给出indexOf方法的签名：

参量

ch：char值, 即单个字符, 例如’一种’

fromIndex：从此处获取char值或子字符串的索引的索引位置

substring：要在此字符串中搜索的子字符串

退货

字符串的索引

Java String indexOf()方法示例

public class IndexOfExample{
public static void main(String args[]){
String s1="this is index of example";
//passing substring
int index1=s1.indexOf("is");//returns the index of is substring
int index2=s1.indexOf("index");//returns the index of index substring
System.out.println(index1+"  "+index2);//2 8

//passing substring with from index
int index3=s1.indexOf("is", 4);//returns the index of is substring after 4th index
System.out.println(index3);//5 i.e. the index of another is

//passing char value
int index4=s1.indexOf('s');//returns the index of s char value
System.out.println(index4);//3
}}

立即测试

2  8
5
3

Java String indexOf（String substring）方法示例

此方法将子字符串作为参数, 并返回该子字符串的第一个字符的索引。

public class IndexOfExample2 {
	public static void main(String[] args) {
		String s1 = "This is indexOf method";  		
		// Passing Substring  
		int index = s1.indexOf("method"); //Returns the index of this substring
		System.out.println("index of substring "+index);		
	}

}

立即测试

index of substring 16

Java字符串indexOf（String substring, int fromIndex）方法示例

此方法将子字符串和索引作为参数, 并返回在给定fromIndex之后出现的第一个字符的索引。

public class IndexOfExample3 {
	public static void main(String[] args) {	
		String s1 = "This is indexOf method";  		
		// Passing substring and index
		int index = s1.indexOf("method", 10); //Returns the index of this substring
		System.out.println("index of substring "+index);
		index = s1.indexOf("method", 20); // It returns -1 if substring does not found
		System.out.println("index of substring "+index);		
	}
}

立即测试

index of substring 16
index of substring -1

Java字符串indexOf（int char, int fromIndex）方法示例

此方法将char和index作为参数, 并返回在给定fromIndex之后出现的第一个字符的索引。

public class IndexOfExample4 {
	public static void main(String[] args) {		
		String s1 = "This is indexOf method";  		
		// Passing char and index from
		int index = s1.indexOf('e', 12); //Returns the index of this char
		System.out.println("index of char "+index);		
	}
}

立即测试

index of char 17