方法indexOf（obj o）在Java中做什么？
java.util.ArrayList类的 indexOf(Object)方法返回此列表中指定元素的首次出现的索引；如果此列表不包含该元素，则返回-1。
示例
import java.util.ArrayList;
public class ArrayListDemo {
public static void main(String[] args) {
ArrayList<String> arrlist = new ArrayList<String>(5);
arrlist.add("G");
arrlist.add("E");
arrlist.add("F");
arrlist.add("M");
System.out.println("Size of list: " + arrlist.size());
for (String value : arrlist) {
System.out.println("Value = " + value);
}
int retval=arrlist.indexOf("E");
System.out.println("The element E is at index " + retval);
}
}输出
Size of list: 4 Value = G Value = E Value = F Value = M The element E is at index 1