8742468051c85b06f0a0af9e3e506b5c T means that the return value is a generic type. Whatever you pass will return the type of data, and a single T means to limit the parameter type you pass. In this case In , through a generic return method, the first data in each collection is obtained, which is achieved by returning the value 8742468051c85b06f0a0af9e3e506b5c T and T two methods.
T Usage
Return value, write T directly to indicate the type of restricted parameter. This method is generally used to jointly operate a class object, and then obtain the collection information inside Something like that.
package com.yellowcong.test; import java.util.ArrayList; import java.util.List; public class Demo2<T> { public static void main(String[] args) { //限制T 为String 类型 Demo2<String> demo = new Demo2<String>(); //获取string类型 List<String> array = new ArrayList<String>(); array.add("test"); array.add("doub"); String str = demo.getListFisrt(array); System.out.println(str); //获取Integer类型 T 为Integer类型 Demo2<Integer> demo2 = new Demo2<Integer>(); List<Integer> nums = new ArrayList<Integer>(); nums.add(12); nums.add(13); Integer num = demo2.getListFisrt(nums); System.out.println(num); } /** * 这个只能传递T类型的数据 * 返回值 就是Demo<T> 实例化传递的对象类型 * @param data * @return */ private T getListFisrt(List<T> data) { if (data == null || data.size() == 0) { return null; } return data.get(0); } }
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