总结：indexOf(String str,int index)方法.从参数指定位置开始，如果index值超过了字符串长度，则返回-1

package com.a.b;import java.io.*;public class Chen {	public static void main(String[] args) throws IOException {		//线程。继承。抽象		String test="After learning the material";		String theStr="arn";		int index=0,theCount=0;		index=test.indexOf(theStr);		while(index>=0){			theCount=theCount+1;					index=index+theStr.length();						index=test.indexOf("arn",index);								}		System.out.println(index);	//	System.out.println("the are "+theCount+" 'arn' in testStr.");	}}