标签：有一个 return ecif with amp sys col spec 开始
String.indexOf()的用途：
返回此字符串中第一个出现的指定的子字符串，如果没有找到则返回-1
源码如下:
/**
* Returns the index within this string of the first occurrence of the
* specified substring.
*
* <p>The returned index is the smallest value <i>k</i> for which:
* <blockquote><pre>
* this.startsWith(str, <i>k</i>)
* </pre></blockquote>
* If no such value of <i>k</i> exists, then {@code -1} is returned.
*
* @param str the substring to search for.
* @return the index of the first occurrence of the specified substring,
* or {@code -1} if there is no such occurrence.
*/
public int indexOf(String str) { return indexOf(str, 0); }
举例1：包含指定子字符串的情况
String str1="abcdef"; String str2="cd"; System.out.println(str1.indexOf(str2));
输出结果：2
举例2：未包含指定子字符串的情况
String str1="abcdef"; String str2="gh"; System.out.println( str1.indexOf(str2) );
输出结果：-1
它还有一个重载的方法：从指定的索引开始，返回此字符串中第一个出现的指定的子字符串，如果没有找到则返回-1
源码如下：
/** * Returns the index within this string of the first occurrence of the * specified substring, starting at the specified index. * * <p>The returned index is the smallest value <i>k</i> for which: * <blockquote><pre> * <i>k</i> >= fromIndex {@code &&} this.startsWith(str, <i>k</i>) * </pre></blockquote> * If no such value of <i>k</i> exists, then {@code -1} is returned. * * @param str the substring to search for. * @param fromIndex the index from which to start the search. * @return the index of the first occurrence of the specified substring, * starting at the specified index, * or {@code -1} if there is no such occurrence. */ public int indexOf(String str, int fromIndex) { return indexOf(value, 0, value.length, str.value, 0, str.value.length, fromIndex); }
举例3：从指定的索引开始，包含指定子字符串的情况
1 String str3="abcdef0abcdef"; 2 String str4="cd"; 3 System.out.println( str3.indexOf(str4,5) );
输出结果：9
举例3：从指定的索引开始，未包含指定子字符串的情况
String str3="abcdef0abcdef"; String str4="gh"; System.out.println( str3.indexOf(str4,5) );
输出结果：-1
标签：有一个 return ecif with amp sys col spec 开始
原文地址：https://www.cnblogs.com/andrew-303/p/11652497.html
