import java.util.ArrayList;
import java.util.List;
/**
* List遇到的问题.
* <p>
* <p>
* <p>
* Created by prd on 2016/03/10.
*/
public class Main {
public static void main(String[] args) {
List<List<String>> lists = new ArrayList<>();
List<String> newlists = new ArrayList<>();
for (int i = 0; i < 5; i++) {
/*
本意是在这里删除newlists里面的所有元素,
全部重新添加.
发现用了clear无效果,但将:
List<String> newlists = new ArrayList<>();
放在循环内则可正常运行.
*/
newlists.clear();
for (int j = 0; j < 10; j++) {
StringBuffer str = new StringBuffer();
str.append("this -> " + j + " , " + i);
newlists.add(str.toString());
}
lists.add(newlists);
}
for (int i = 0; i < lists.size(); i++) {
for (int j = 0; j < lists.get(i).size(); j++) {
System.out.println(lists.get(i).get(j));
}
System.out.println("-------------------------------");
}
}
}
错误的运行结果【注意最后一个数字】：
this -> 0 , 4
this -> 1 , 4
this -> 2 , 4
this -> 3 , 4
this -> 4 , 4
this -> 5 , 4
this -> 6 , 4
this -> 7 , 4
this -> 8 , 4
this -> 9 , 4
-------------------------------
this -> 0 , 4
this -> 1 , 4
this -> 2 , 4
this -> 3 , 4
this -> 4 , 4
this -> 5 , 4
this -> 6 , 4
this -> 7 , 4
this -> 8 , 4
this -> 9 , 4
-------------------------------
this -> 0 , 4
this -> 1 , 4
this -> 2 , 4
this -> 3 , 4
this -> 4 , 4
this -> 5 , 4
this -> 6 , 4
this -> 7 , 4
this -> 8 , 4
this -> 9 , 4
-------------------------------
this -> 0 , 4
this -> 1 , 4
this -> 2 , 4
this -> 3 , 4
this -> 4 , 4
this -> 5 , 4
this -> 6 , 4
this -> 7 , 4
this -> 8 , 4
this -> 9 , 4
-------------------------------
this -> 0 , 4
this -> 1 , 4
this -> 2 , 4
this -> 3 , 4
this -> 4 , 4
this -> 5 , 4
this -> 6 , 4
this -> 7 , 4
this -> 8 , 4
this -> 9 , 4
-------------------------------
下面是可以正常运行的代码：
import java.util.ArrayList;
import java.util.List;
/**
* List遇到的问题.
* <p>
* <p>
* <p>
* Created by prd on 2016/03/10.
*/
public class Main {
public static void main(String[] args) {
List<List<String>> lists = new ArrayList<>();
for (int i = 0; i < 5; i++) {
/*
本意是在这里删除newlists里面的所有元素,
全部重新添加.
发现用了clear无效果,但将:
List<String> newlists = new ArrayList<>();
放在循环内则可正常运行.
*/
List<String> newlists = new ArrayList<>();
//newlists.clear();
for (int j = 0; j < 10; j++) {
StringBuffer str = new StringBuffer();
str.append("this -> " + j + " , " + i);
newlists.add(str.toString());
}
lists.add(newlists);
}
for (int i = 0; i < lists.size(); i++) {
for (int j = 0; j < lists.get(i).size(); j++) {
System.out.println(lists.get(i).get(j));
}
System.out.println("-------------------------------");
}
}
}
想要的结果：
this -> 0 , 0
this -> 1 , 0
this -> 2 , 0
this -> 3 , 0
this -> 4 , 0
this -> 5 , 0
this -> 6 , 0
this -> 7 , 0
this -> 8 , 0
this -> 9 , 0
-------------------------------
this -> 0 , 1
this -> 1 , 1
this -> 2 , 1
this -> 3 , 1
this -> 4 , 1
this -> 5 , 1
this -> 6 , 1
this -> 7 , 1
this -> 8 , 1
this -> 9 , 1
-------------------------------
this -> 0 , 2
this -> 1 , 2
this -> 2 , 2
this -> 3 , 2
this -> 4 , 2
this -> 5 , 2
this -> 6 , 2
this -> 7 , 2
this -> 8 , 2
this -> 9 , 2
-------------------------------
this -> 0 , 3
this -> 1 , 3
this -> 2 , 3
this -> 3 , 3
this -> 4 , 3
this -> 5 , 3
this -> 6 , 3
this -> 7 , 3
this -> 8 , 3
this -> 9 , 3
-------------------------------
this -> 0 , 4
this -> 1 , 4
this -> 2 , 4
this -> 3 , 4
this -> 4 , 4
this -> 5 , 4
this -> 6 , 4
this -> 7 , 4
this -> 8 , 4
this -> 9 , 4
-------------------------------
有大神可以解释下这是为啥吗？谢谢。
