java ArrayList 中的 set()
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set() in ArrayList
提问by suresh
I am new to Java, please help me.
我是 Java 新手，请帮助我。
My program is
我的程序是
import java.util.*;
import java.lang.*;
class Test
{
public static void main(String[] args)
{
ArrayList al=new ArrayList();
al.add("a");
al.add("b");
for(int i=1;i<=10;i++)
{
al.add(i);
}
al.remove("a");
al.set(1,"c");
for(int j=3;j<=al.size();j++)
{
al.set(j,"z");
}
System.out.println(al);
}
};
in above any mistake........plz help me
以上任何错误......请帮助我
回答by Sean Patrick Floyd
a) You need to make the class public to run it:
a) 您需要公开该类才能运行它：
public class Test
{
b) the last semi-colon is a syntax errorNo it's not, it's just unnecessary noise.
b) 最后一个分号是语法错误不，不是，这只是不必要的噪音。
c) This fails with an IndexOutOfBoundsException:
c) 这失败了IndexOutOfBoundsException：
for(int j = 3; j <= al.size(); j++){
al.set(j, "z");
}
It needs to be:
它必须是：
for(int j = 3; j < al.size(); j++){
al.set(j, "z");
}
Explanation:List Indexes are zero-based, so the highest position in a List with n elements is n-1
说明：列表索引是从零开始的，所以在一个有 n 个元素的 List 中的最高位置是 n-1
BTW, the above code can be written in a more elegant way like this:
顺便说一句，上面的代码可以用更优雅的方式写成这样：
Collections.fill(al.subList(3, al.size()), "z");
Reference:
参考：
回答by roghughe
This code will throw an IndexOutOfBounds exception because of the line:
由于以下行，此代码将引发 IndexOutOfBounds 异常：
for (int j = 3; j <= al.size(); j++) {
to fix it, you need to change it to:
要修复它，您需要将其更改为：
for (int j = 3; j < al.size(); j++) {
This is because the <= means that your for loop iterates over the end of the list.
这是因为 <= 表示您的 for 循环遍历列表的末尾。
回答by user unknown
List~ and Arrayindices start at 0, not 1. So if you have a list of 3 Elements, they go from index: 0, 1, 2. So you normally iterate from (i = 0; i < list.size (); ++i). Less than, not less/equal.
List~ 和 Arrayindices 从 0 开始，而不是 1。所以如果你有一个包含 3 个元素的列表，它们从索引：0, 1, 2 开始。所以你通常从 (i = 0; i < list.size (); 开始迭代。 ++i)。小于，不小于/等于。
for (int j=3; j < al.size (); j++)
回答by Lalchand
1.The semicolon in the last line
1.最后一行的分号
2.change the code from
2.更改代码
for(int j=3;j<=al.size();j++)
to
到
for(int j=3;j<al.size();j++)
Arraylist are always accessed from from 0th index to less than the size of the array.
Arraylist 总是从第 0 个索引到小于数组的大小访问。
回答by Yuriy Semen
I think it is necessary to change also the start index from 3 to 2:
我认为有必要将起始索引也从 3 更改为 2：
for (int j=2; j < al.size (); j++)
