上楼梯每次只能迈一阶或者两阶，有几种方法？ 斐波那契数列：
public int fbnq(int n) { if (n == 1) { return 1; } else if (n == 2) { return 1; } else { return fbnq(n - 1) + fbnq(n - 2); } }两种单例模式？ 懒汉式：
public class Singleton1 { private Singleton1() { } private static Singleton1 s = null; public static Singleton1 getInstance() { if (s == null) { s = new Singleton1(); } return s; } }俄汉式：
public class Singleton2 { private Singleton2() { } private static Singleton2 s = new Singleton2(); public static Singleton2 getInstance() { return s; } }字符排序？ 冒泡排序：
for (int i = 0; i < chs.length - 1; i++) { for (int j = 0; j < chs.length - 1 - i; j++) { if (chs[j] > chs[j + 1]) { char temp = chs[j]; chs[j] = chs[j + 1]; chs[j + 1] = temp; } } }选择排序：
for (int i = 0; i < chs.length - 1; i++) { for (int j = i + 1; j < chs.length; j++) { if (chs[j] < chs[i]) { char temp = chs[j]; chs[j] = chs[i]; chs[i] = temp; } } }Arrays工具类排序：
Arrays.sort(chs);获取一个字符串在另一个字符串中出现的次数？
public int getCount(String mainStr, String subStr) { if (mainStr.length() >= subStr.length()) { int count = 0; // 记录次数 int index = 0; // while((index = mainStr.indexOf(subStr)) != -1){ // count++; // mainStr = mainStr.substring(index + subStr.length()); // } // 改进： while ((index = mainStr.indexOf(subStr, index)) != -1) { index += subStr.length(); count++; } return count; } else { return 0; } } @Test public void testGetCount() { String str1 = "cdabkkcadkabkebfkabkskab"; String str2 = "ab"; int count = getCount(str1, str2); System.out.println(count); }获取最大相同子串？
public String getMaxSameString(String str1, String str2) { if (str1 != null && str2 != null) { String maxStr = (str1.length() >= str2.length()) ? str1 : str2; String minStr = (str1.length() < str2.length()) ? str1 : str2; int len = minStr.length(); // 决定了比较的轮数 for (int i = 0; i < len; i++) { // 0 1 2 3 4 此层循环决定要去几个字符 for (int x = 0, y = len - i; y <= len; x++, y++) { if (maxStr.contains(minStr.substring(x, y))) { return minStr.substring(x, y); } } } } return null; } @Test public void testGetMaxSameSubString() { String str1 = "abcwerthelloyuiodef"; String str2 = "cvhellobnmiodef"; String str = getMaxSameString(str1, str2); System.out.println(str); }// 如果存在多个长度相同的最大相同子串：使用ArrayList
public List<String> getMaxSameSubString1(String str1, String str2) { if (str1 != null && str2 != null) { List<String> list = new ArrayList<String>(); String maxString = (str1.length() > str2.length()) ? str1 : str2; String minString = (str1.length() > str2.length()) ? str2 : str1; int len = minString.length(); for (int i = 0; i < len; i++) { for (int x = 0, y = len - i; y <= len; x++, y++) { String subString = minString.substring(x, y); if (maxString.contains(subString)) { list.add(subString); } } if (list.size() != 0) { break; } } return list; } return null; }随机生成30个数，范围2-100，获取其中的质数？
ArrayList<Integer> arrayList = new ArrayList<Integer>(); ArrayList<Integer> arrayList2 = new ArrayList<Integer>(); for (int i = 0; i < 30; i++) { int randomNum = (int) (Math.random() * (100 - 2 + 1) + 2); arrayList.add(randomNum); boolean flag = true; for (int j = 2; j < Math.sqrt(randomNum); j++) { // 范围：开方 if (randomNum % j == 0) { flag = false; break; } } if (flag) { arrayList2.add(randomNum); } } System.out.println("随机数为：\n" + arrayList.toString()); System.out.println("质数为：\n" + arrayList2.toString());解决线程安全问题(传入公共对像作为同步监视器)？
public class WindowTest { public static void main(String[] args) { Window w = new Window(); Thread t1 = new Thread(w); Thread t2 = new Thread(w); Thread t3 = new Thread(w); t1.setName("窗口1"); t2.setName("窗口2"); t3.setName("窗口3"); t1.start(); t2.start(); t3.start(); } } class Window implements Runnable { private int ticket = 100; @Override public void run() { for(int i = 1;i <= 100;i++){ show(); } } public synchronized void show() { // 此时的同步监视器是this if (ticket > 0) { try { Thread.sleep(30); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName() + "售票，票号为:" + ticket); ticket--; } } }List去重4种方式？ 1).双for相同remove：
for (int i = 0; i < list.size(); i++) { for (int j = i + 1; j < list.size(); j++) { if (list.get(i) == list.get(j)) { list.remove(j); j--; // 因为删除，所以角标前移 } } }2).list contains判断：
for (int i = 0; i < list1.size(); i++) { if (!list2.contains(list1.get(i))) { list2.add(list1.get(i)); } }3).List转Set：
HashSet<String> set = new HashSet<>(list); list.clear(); list.addAll(set);4).Set add返回值判断：
for (int i = 0; i < list1.size(); i++) { if (set.add(list1.get(i))) { list2.add(list1.get(i)); } }Map的4种遍历方法？ 1).keySet遍历key：
for (Object in : map.keySet()) { System.out.println(map.get(in)); }2).迭代器遍历entry：
Iterator<Map.Entry<Integer, String>> it = map.entrySet().iterator(); while (it.hasNext()) { Map.Entry<Integer, String> entry = it.next(); System.out.println(entry.getKey()); System.out.println(entry.getValue()); }3).entrySet遍历entry
for (Map.Entry<Integer, String> entry : map.entrySet()) { System.out.println(entry.getKey()); System.out.println(entry.getValue()); }4).values遍历value
for (String v : map.values()) { System.out.println(v); }File文件复制？
public void streamCopy() { FileInputStream fileInputStream = null; FileOutputStream fileOutputStream = null; try { fileInputStream = new FileInputStream("D:\\a.jpg"); fileOutputStream = new FileOutputStream("D:\\b.jpg"); int len; byte[] temp = new byte[1024]; while ((len = fileInputStream.read(temp)) != -1) { fileOutputStream.write(temp, 0, len); } } catch (IOException e) { e.printStackTrace(); } finally { if (fileOutputStream != null) { try { fileOutputStream.close(); } catch (IOException e) { e.printStackTrace(); } } if (fileInputStream != null) { try { fileInputStream.close(); } catch (IOException e) { e.printStackTrace(); } } } } public void bufferedCopy() { BufferedInputStream bis = null; BufferedOutputStream bos = null; try { bis = new BufferedInputStream(new FileInputStream("day26.iml")); bos = new BufferedOutputStream(new FileOutputStream("day26_copy.iml")); byte[] temp = new byte[1024]; int len; while ((len = bis.read(temp)) != -1) { bos.write(temp, 0, len); } } catch (IOException e) { e.printStackTrace(); } finally { if (bos != null) { try { bos.close(); } catch (IOException e) { e.printStackTrace(); } } if (bis == null) { try { bis.close(); } catch (IOException e) { e.printStackTrace(); } } } }将gbk格式的文件转换为utf-8格式存储？
public void transform() { InputStreamReader isr = null; OutputStreamWriter osw = null; try { isr = new InputStreamReader(new FileInputStream("gbkBook.txt"), "gbk"); osw = new OutputStreamWriter(new FileOutputStream("utf8Book.txt")); char[] temp = new char[1024]; int len; while ((len = isr.read(temp)) != -1) { osw.write(temp, 0, len); } } catch (IOException e) { e.printStackTrace(); } finally { try { if (osw != null) { osw.close(); } } catch (IOException e) { e.printStackTrace(); } try { if (isr != null) { isr.close(); } } catch (IOException e) { e.printStackTrace(); } } }TCP编程：服务器-客户端发送文件/聊天？ // 从客户端发送文件给服务端，服务端保存到本地，并返回“发送成功”给客户端。
@Test public void client() throws IOException { Socket socket = new Socket(InetAddress.getByName("127.0.0.1"), 8989); // 创建ServerSocket FileInputStream fis = new FileInputStream("baby.jpg"); OutputStream os = socket.getOutputStream(); byte[] buffer = new byte[1024]; int len; while((len = fis.read(buffer)) != -1){ os.write(buffer,0,len); } System.out.println("client-------1"); socket.shutdownOutput(); // 显式的关闭输出流 //接收来自于服务器端的数据,并显示 InputStream is = socket.getInputStream(); ByteArrayOutputStream baos = new ByteArrayOutputStream(); byte[] newBuf = new byte[10]; int newLen; while((newLen = is.read(newBuf)) != -1){ baos.write(newBuf,0,newLen); } System.out.println(baos.toString()); // 关闭流(省略try-catch-finally) is.close(); baos.close(); os.close(); fis.close(); socket.close(); } @Test public void server() throws IOException { ServerSocket serverSocket = new ServerSocket(8989); Socket socket = serverSocket.accept(); InputStream is = socket.getInputStream(); FileOutputStream fos = new FileOutputStream("src/babyabc.jpg"); byte[] buffer = new byte[1024]; int len; while((len = is.read(buffer)) != -1){ fos.write(buffer,0,len); } System.out.println("server-------1"); OutputStream os = socket.getOutputStream(); os.write("收到你的靓照，非常的漂亮！".getBytes()); // 服务器给客户端反馈数据 // 关闭流 os.close(); fos.close(); is.close(); socket.close(); //serverSocket.close(); // 关闭服务器 }URL编程：下载文件？
HttpURLConnection urlConnection = null; InputStream is = null; FileOutputStream fos = null; try { URL url = new URL("http://localhost:8080/examples/playgirl.jpg"); urlConnection = (HttpURLConnection) url.openConnection(); is = urlConnection.getInputStream(); fos = new FileOutputStream("playgirl.jpg"); byte[] buffer = new byte[1024]; int len; while ((len = is.read(buffer)) != -1) { fos.write(buffer, 0, len); } System.out.println("下载成功"); } catch (IOException e) { e.printStackTrace(); } finally { try { if (is != null) is.close(); } catch (IOException e) { e.printStackTrace(); } try { if (fos != null) fos.close(); } catch (IOException e) { e.printStackTrace(); } if (urlConnection != null) urlConnection.disconnect(); }获取Class的四种方式？ ①Class clazz = Person.class; // 调用类的静态属性：class，不会执行静态代码块 ②Person p = new Person();Class clazz2 = p.getClass(); // 调用对象的方法：getClass()，new会执行静态代码块 ③Class class3 = Class.forName(“com.atguigu.test.Person”); // 调用Class的静态方法：forName(String className)，会执行静态代码块 ④ClassLoader cl = Reflection.class.getClassLoader();Class class4 = cl.loadClass(“com.atguigu.test.Person”); // 使用类的加载器，不会执行静态代码块 1 3 4相似，一般选3
读取配置文件的两种方式？ 方式一：
FileInputStream fis = new FileInputStream("jdbc.properties"); Properties pros = new Properties(); pros.load(fis1); String name = pros.getProperty("name");方式二：
InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("jdbc1.properties"); Properties pros = new Properties(); pros.load(is); String name = pros.getProperty("name");