请问为什么用get（i）方法不行，求帮忙看下是哪里的问题~谢谢

[baidu_37686877]

import java.util.ArrayList;
import java.util.List;
import java.util.Collection;
public class ArrayListDemo03 {
public static void main(String args[]){
List<String> allList=null;
allList =new ArrayList<String>();
allList.add("Hello");
allList.add("World");
allList.add(0,"YuuW24k");
Collection<String> allCollection=null;
allCollection =new ArrayList<String>();
allCollection.add("Sad");
allCollection.add("or");
allCollection.add("Happy");
allList.addAll(1, allCollection);
System.out.println(allList);
System.out.print("由前向后输出：");
for(int i=0;i<=allList.size();i++){
System.out.print(allList.get(i)+",");
}
System.out.print("\n由后向前输出：");
for(int i=allList.size();i<=0;i--){
System.out.print(allList.get(i)+",");
}
}
}

[李德胜1995]

下面两个循环改成这样就可以了。。。

for(int i=0;i<allList.size();i++){
			System.out.print(allList.get(i)+",");
	}
		System.out.print("\n由后向前输出：");
		
		for(int i=allList.size()-1;i>=0;i--){
			System.out.print(allList.get(i)+",");
		}

[baidu_37686877]

[YuuW24k, Sad, or, Happy, Hello, World] 由前向后输出：YuuW24k,Sad,or,Happy,Hello,World,Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 6, Size: 6 at java.util.ArrayList.rangeCheck(Unknown Source) at java.util.ArrayList.get(Unknown Source) at ArrayListDemo03.main(ArrayListDemo03.java:20) 还是不行哦~

[abcdefghiijklmnopqrs]

for (int i = 0; i < allList.size(); i++) {
			System.out.print(allList.get(i) + ",");
		}
		System.out.print("\n由后向前输出：");
		for (int i = allList.size()-1; i >= 0; i--) {
			System.out.print(allList.get(i) + ",");
		}

[ryuugu_rena]

应该i<alllist.size()，你写的越界了

[fmaidou]

引用 2 楼 baidu_37686877 的回复:

[YuuW24k, Sad, or, Happy, Hello, World] 由前向后输出：YuuW24k,Sad,or,Happy,Hello,World,Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 6, Size: 6 at java.util.ArrayList.rangeCheck(Unknown Source) at java.util.ArrayList.get(Unknown Source) at ArrayListDemo03.main(ArrayListDemo03.java:20) 还是不行哦~

你是没有减1吧 for (int i = allList.size()-1; i >= 0; i--) { System.out.print(allList.get(i) + ","); }

[baidu_37686877]

已经弄懂了 谢谢大家~

[zs808]

引用 4 楼 ryuugu_rena 的回复:

应该i<alllist.size()，你写的越界了

正解，下标遍历别忘了是0到length-1。这个问题以前也被坑过好多次啊啊啊啊

[qq_29690821]

现在的开发工具（eclipse等），越界没有错误提示吗？