英文:
How to delete last element in array and put new in front?
问题
以下是翻译好的部分：
我对Java有一个问题。我刚开始学习Java，我的谷歌搜索得到了许多结果，但没有一个是最终的帮助。
我创建了一个类来跟踪历史信息。我有不同的值对应不同的天数，需要定期更新它们。我想要跟踪最近的30天，并创建了一个有30个元素的数组。当我调用我的 'shift' 函数时，我想丢弃最后n个元素，并在前面插入零。以下是一个包含5天的简单示例：
public class Testclass {private int[] histInfo;public Element(){this.histInfo = new int[5];}public void shift_histInfo(long m){// 进行操作}}
我希望 shift_histInfo 函数的操作是：
输入：histInfo = [50,21,1,45,901]操作：shift_histInfo(2);结果：histInfo = [0,0,50,21,1]
如果您认为有更加优雅或高效的方法，我将非常感激您提供的任何帮助和富有启发性的思路。
最好的祝愿 
英文:
I have a question concerning Java. I started up new to Java and my google search brought many results but non was the final help.
I created a class to track historical information. I have different values for different days and need to update them un a regular basis. I want to keep track of the last 30 days and created an array with 30 elements. When I call my 'shift' function I want to drop the last n elements and put zeros in front. Here is a minial example for 5 days:
public class Testclass {private int[] histInfo;public Element(){this.histInfo = new int[5];}public void shift_histInfo(long m){//do magic}}
What I want shift to do is
INPUT:histInfo = [50,21,1,45,901]OPERATION:shift_histInfo(2);RESULT:histInfo = [0,0,50,21,1]
I am thankfull for every kind of help you can support as well for thought-provoking impulses if you think that there is a way more elegant or efficient way.
Best
答案1
得分: 1
除非有非常严格的性能限制，使用标准的集合类就能完成任务。看一下 java.util.LinkedList。
作为一个编程练习，你可以考虑创建一个环形缓冲区（ring buffer）。这个想法是为了避免在每次插入时复制数组。
保持一个 oldestIndex 值。
写入时只需替换 item[oldestIndex] 并增加 oldestIndex。
要进行迭代，从 oldestIndex 开始，并使用增量方法来处理回绕到数组开头。
int nextIndex(int current) {return (current + 1) % arrayLength;}
编写一个好的封装类来隐藏所有这些将是一个不错的练习。
英文:
Unless there are very tight performance constraints using the standard Collection classes will get the job done. Have a look at java.util.LinkedList.
As a programming exercise you might consider creating a ring buffer. The idea being to avoid copying the array on every insertion.
Keep a oldestIndex value.
When writing simply replace item[oldestIndex] and increment oldestIndex.
To iterate you start at oldestIndex and use an increment method to deal with wrapping round to the start of the array.
int nextIndex(int current) {return (current + 1) % arrayLength;}
Writing a nice encapsulating class to hide all this would be a good exercise.
答案2
得分: 0
public static void shift_histInfo(long m){int[] myIntArray = {50, 21, 1, 45, 901};int[] myIntArray2 = new int[myIntArray.length];for (int j = 0; j < myIntArray.length; j++) {int temp = (int) (j + m);if (temp >= myIntArray.length) {temp = temp - myIntArray.length;myIntArray2[temp] = 0;} else {myIntArray2[temp] = myIntArray[j];}}for (int j = 0; j < myIntArray2.length; j++) {System.out.println(myIntArray2[j]);}}
输出：
当调用 shift_histInfo(2) 时，
[0, 0, 50, 21, 1]
英文:
You can try this :
public static void shift_histInfo(long m){int[] myIntArray = {50,21,1,45,901};int[] myIntArray2 = {50,21,1,45,901};for (int j=0 ;j< myIntArray.length ; j++){int temp = (int) (j+m);if (temp >= myIntArray.length){temp = temp - myIntArray.length;myIntArray2[temp] = 0;} else {myIntArray2[temp] = myIntArray[j];}}for (int j=0 ;j< myIntArray2.length ; j++){System.out.println(myIntArray2[j]);}}
Output :
when shift_histInfo(2) ,
[0,0,50,21,1]
答案3
得分: 0
int[] array = {1, 2, 3, 4, 5, 6};int removelength = 2;int e = 1;while (e <= removelength) {for (int i = 1; i < array.length; i++)array[array.length - i] = array[array.length - i - 1];e++;}for (int i = 0; i < removelength; i++) {array[i] = 0;}for (int g : array) {System.out.print(g);}
英文:
int[] array={1,2,3,4,5,6};int removelength=2;int e=1;while(e<=removelength) {for(int i=1;i<array.length;i++)array[array.length-i]=array[array.length-i-1];e++;}for(int i=0;i<removelength;i++) {array[i]=0;}for(int g:array){System.out.print(g);}
答案4
得分: 0
private int[] histInfo;public void shift_histInfo(long m) {int n = (int) m;this.histInfo = new int[]{1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13,14,15,1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13,14,15};int length = this.histInfo.length;int[] changedInfo = new int[length];if (length - n >= 0) System.arraycopy(histInfo, 0, changedInfo, n + 0, length - n);histInfo = changedInfo.clone();System.out.println("Remove: " + n + " - " + Arrays.toString(changedInfo) + "\n");}public static void main(String[] args) {Main main = new Main();main.shift_histInfo(0);main.shift_histInfo(30);main.shift_histInfo(1);main.shift_histInfo(15);main.shift_histInfo(29);}
Remove: 0 - [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]Remove: 30 - [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]Remove: 1 - [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]Remove: 15 - [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]Remove: 29 - [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1]
英文:
For constraints that you wanted, although I did initialise the data in the same method instead of Element(). I don't know why the parameter is of type long so I left it and made an int local variable.
All it does is copy the index value over to the new array starting at m then increments/iterates until the end of the array.
You can also make the method return type int[] and then simply return changedInfo array. Instead of histInfo = changedInfo.clone();
private int[] histInfo;public void shift_histInfo(long m) {int n = (int) m;this.histInfo = new int[]{1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13,14,15,1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13,14,15};int length = this.histInfo.length;int[] changedInfo = new int[length];if (length - n >= 0) System.arraycopy(histInfo, 0, changedInfo, n + 0, length - n); //Edit: shortened to one line.histInfo = changedInfo.clone();System.out.println("Remove: " + n + " - " + Arrays.toString(changedInfo) + "\n");}public static void main(String[] args) {Main main = new Main();main.shift_histInfo(0);main.shift_histInfo(30);main.shift_histInfo(1);main.shift_histInfo(15);main.shift_histInfo(29);}
println:
Remove: 0 - [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]Remove: 30 - [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]Remove: 1 - [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]Remove: 15 - [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]Remove: 29 - [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1]
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