List<String> fileList = new ArrayList<String>();
时间: 2023-11-11 19:43:51 浏览: 33
这段代码创建了一个 ArrayList 类型的 fileList 对象,用来存储 String 类型的数据。这个对象还没有任何元素,因为它没有被初始化。可以通过调用 add() 方法向 fileList 中添加元素,例如:
fileList.add("file1.txt");
fileList.add("file2.txt");
fileList.add("file3.txt");
这样就向 fileList 中添加了三个字符串元素。可以使用 get() 方法获取列表中的元素,例如:
String firstFile = fileList.get(0);
System.out.println(firstFile); // 输出:file1.txt
注意,列表的索引从 0 开始。可以使用 size() 方法获取列表的大小,也就是元素的数量,例如:
int numFiles = fileList.size();
System.out.println("Number of files: " + numFiles); // 输出:Number of files: 3
相关问题
在Android中写一段java代码使用dhash算法找出List<File> fileList这个fileList中所有具有相似图片的图片文件,并将它们保存在Map<String, List<String>>中
以下是使用dhash算法在Android中找出具有相似图片的文件的Java代码,将它们保存在Map<String, List<String>>中:
```java
import java.io.File;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class DHashAlgorithm {
// DHash算法的阈值
private static final int THRESHOLD = 5;
// 获取图片的dhash值
private static String getDHash(File file) {
Bitmap bitmap = BitmapFactory.decodeFile(file.getAbsolutePath());
bitmap = Bitmap.createScaledBitmap(bitmap, 9, 8, true);
int[] pixels = new int[bitmap.getWidth() * bitmap.getHeight()];
bitmap.getPixels(pixels, 0, bitmap.getWidth(), 0, 0, bitmap.getWidth(), bitmap.getHeight());
StringBuilder sb = new StringBuilder();
for (int i = 0; i < pixels.length; i++) {
sb.append((pixels[i] & 0xff) > (pixels[i + 1] & 0xff) ? "1" : "0");
}
String dHash = "";
for (int i = 0; i < sb.length(); i += 4) {
int decimal = Integer.parseInt(sb.substring(i, i + 4), 2);
dHash += Integer.toHexString(decimal);
}
return dHash;
}
// 计算dhash值之间的汉明距离
private static int getHammingDistance(String dHash1, String dHash2) {
int hammingDistance = 0;
for (int i = 0; i < dHash1.length(); i++) {
if (dHash1.charAt(i) != dHash2.charAt(i)) {
hammingDistance++;
}
}
return hammingDistance;
}
// 找出具有相似图片的文件,并将它们保存在Map<String, List<String>>中
public static Map<String, List<String>> findSimilarImages(List<File> fileList) {
Map<String, List<String>> imageMap = new HashMap<>();
for (int i = 0; i < fileList.size(); i++) {
File file1 = fileList.get(i);
String dHash1 = getDHash(file1);
List<String> similarImages = new ArrayList<>();
for (int j = i + 1; j < fileList.size(); j++) {
File file2 = fileList.get(j);
String dHash2 = getDHash(file2);
int hammingDistance = getHammingDistance(dHash1, dHash2);
if (hammingDistance <= THRESHOLD) {
similarImages.add(file2.getAbsolutePath());
}
}
if (similarImages.size() > 0) {
imageMap.put(file1.getAbsolutePath(), similarImages);
}
}
return imageMap;
}
}
```
使用方法:
```java
List<File> fileList = new ArrayList<>();
fileList.add(new File("/path/to/image1.jpg"));
fileList.add(new File("/path/to/image2.jpg"));
fileList.add(new File("/path/to/image3.jpg"));
Map<String, List<String>> imageMap = DHashAlgorithm.findSimilarImages(fileList);
```
其中,fileList是包含所有图片文件的列表,imageMap是保存具有相似图片的文件的Map对象。如果两张图片的dhash值之间的汉明距离小于等于THRESHOLD(默认为5),则认为它们是相似的。
TbRiskUnit pojo= new TbRiskUnit(); CurrentLoginUser user = AppUtil.getCurrentUser(); if (user.getUserType() == 2) { pojo.setCorpId(user.getCorpId()); } List<TbRiskUnit> list = unitService.getQrCodeList(pojo); String[] filePath = new String[list.size()]; List<File> fileList = new ArrayList<>(); for (int i = 0; i < list.size(); i++) { TbRiskUnit qrCode = list.get(i); filePath[i] = qrCode.getImageUrl(); fileList.add(new File(qrCode.getImageUrl())); } response.setHeader("content-type", "application/octet-stream"); response.setContentType("application/octet-stream"); response.setHeader(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=download.zip"); ZipUtils.downloadZip(response.getOutputStream(), fileList); }这段代码中我的ImageUrl有多个值我怎么把他用逗号分隔开传进String[list.size()]中呢
可以使用 StringBuilder 来实现将多个 ImageUrl 用逗号隔开的操作。可以在 for 循环中使用 StringBuilder 将所有 ImageUrl 拼接在一起,最后将拼接好的字符串通过 split() 方法转成数组,赋值给 filePath 数组。代码示例如下:
```
TbRiskUnit pojo = new TbRiskUnit();
CurrentLoginUser user = AppUtil.getCurrentUser();
if (user.getUserType() == 2) {
pojo.setCorpId(user.getCorpId());
}
List<TbRiskUnit> list = unitService.getQrCodeList(pojo);
StringBuilder sb = new StringBuilder();
List<File> fileList = new ArrayList<>();
for (int i = 0; i < list.size(); i++) {
TbRiskUnit qrCode = list.get(i);
sb.append(qrCode.getImageUrl()).append(",");
fileList.add(new File(qrCode.getImageUrl()));
}
String[] filePath = sb.toString().split(",");
response.setHeader("content-type", "application/octet-stream");
response.setContentType("application/octet-stream");
response.setHeader(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=download.zip");
ZipUtils.downloadZip(response.getOutputStream(), fileList);
```