//输入输出
Scanner in = new Scanner(System.in);
int a = in.nextInt();
int b = in.next();
System.out.println(in.nextLine());
//输入流 InputStream
System.in.read(buffer); //读取输入流存到buffer（byte[]类型）中
System.in.read(); //读一个字节，若结尾返回-1
System.in.read(buffer, int off, int len); // 读len个字节，从buffer[off]开始存
System.in.skip(n); //输入流跳过n个字节
System.in.available();
System.in.mark(); //标记
System.in.reset(); //返回标记处
System.in.markSupported; //是否支持标记
System.in.close(); //关闭输入流
//类java.io.StreamTokenizer可以获取输入流并将其分析为Token(标记)。StreamTokenizer的nextToken方法将读取下一个标记,下一个标记的类型在ttype字段中返回。关于令牌的附加信息可能是在nval字段或标记生成器的sval 字段，结束标志为TT_EOF。
StreamTokenizer st = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
st.nextToken();
int m=(int)st.nval;
//输出流 OutputStream
System.out.write(int b);
System.out.write(byte[] b);
System.out.write(byte[] b, int off, int len);
System.out.flush();
System.out.close();
//文件流
//二进制数据读写（字节流）
FileOutputStream out = new FileOutputStream("a.txt"); //根据字节读写数据
out.write(buffer);
out.close();
FileInputStream in = new FileInputStream("a.txt");
in.read();
in.close();
DataOutputStream out = new DataOutputStream(
new BufferedOutputStream(
new FileOutputStream("a.txt"))); //读写基本类型数据
out.writeInt(int a);
DataInputStream in = new DataInputStream(
new BufferedInputStream(
new FileInputStream("a.txt")));
in.readInt();
//文本数据读写（字符流）
PrintWriter out = new PrintWriter(
new BufferedWriter(
new OutputStreamWriter(
new FileOutputStream("a.txt")))); //输出文本数据
out.println("abcdefg");
out.format("格式",...);
out.printf("格式", ...);
out.print(基本类型);
BufferedReader in = new BufferedReader(
new InputStreamReader(
new FileInputStream("a.txt"))); //读文本数据
String line = in.readLine();
in.getLineNumber();
FileReader in = new FileReader(String fileName); //在给定从中读取数据的文件名的情况下新建FileReader
FileReader in = new FileReader(File file); //在给定从中读取数据的File的情况下新建FileReader
//转换编码
InputStreamReader(InputStream in, String charsetName); //创建使用指定字符集的InputStreamReader
//网络端口连接读写数据
Socket socket = new Socket(InetAddress.getByName("localhost"), 12345); //建立与本地12345端口的连接
PrintWriter out = new PrintWriter(
new BufferedWriter(
new OutputStreamWriter(
socket.getOutputStream()))); //建立对socket的输出流
//读写对象
class Student implements Serializable {
...
} //类实现Serializable串行化接口
ObjectOutputStream out = new ObjectOutputStream(
new FileOutputStream("a.dat")); //对象输出流
out.writeObject(Student stu1);
ObjectInputStream in = new ObjectInputStream(
new FileInputStream("a.dat"); //对象输入流
out.readObject(Student stu2);
//字符串操作
String s = new String();
s.equals("abc");
s1.compareTo(s2);
s.substring(n);
s.substring(n1, n2);
s.charAt(index);
s.indexOf(c);
s.indexOf(c, n);
s.indexOf(t); //也可以寻找字符串位置
s.lastIndexOf(c); //从右边开始找
s.startsWith(t); //是否由字符串t开始
s.endsWith(t); //是否由字符串t结尾
s.trim(); //把字符串两端的空格删掉
s.replace(c1, c2); //把s中所有的c1都换成c2
s.toLowerCase(); //把s中所有的大写字母换成小写字母
s.toUpperCase(); //把s中所有的小写字母换成大写字母
s.split(" "); //按某个字符（比如空格）将字符串提取出来
StringBuffer sb = new StringBuffer(); //用作字符串缓存器
StringBuilder sb = new StringBuilder(); //与StringBuffer相似，没有实现线程安全功能
sb.append(""); //增加一个字符串
sb.insert(n, ""); //插入字符串
sb.toString(); //转换成字符串
String.format("Hello, %s. Next year, you‘ll be %d", name, age); //格式化字符串
//Java中的包装类
Integer类的常用方法：
byteValue() //将Integer转换为byte类型
doubleValue() //将Integer转换为double类型
...
基本类型转换为字符串：
Integer.toString(int n) //转换为字符串类型
String.valueOf(int n) //int类型转换为字符串类型
字符串转换为基本类型：
Integer.parseInt(Stirng s) //将字符串转换为int类型
Integer.valueOf(String s) //将字符串转换为Integer类型
//时间类
Date d = new Date(); //java.util包中，默认无参构建当前时间
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); //java.text包中，创建目标格式对象
String today = sdf.format(d); //将时间格式化为指定格式
Date date = sdf.parse(today); //将字符串按指定格式转化为时间
-------
Calendar c = Calendar.getInstance(); //java.util.Calendar，创建Calendar对象，初始化为当前时间
int year = c.get(Calendar.YEAR);
int month = c.get(Calendar.MONTH)+1; //0表示1月份
int day = c.get(Calendar.DAY_OF_MONTH);
int hour = c.get(Calendar.HOUR_OF_DAY);
int minute = c.get(Calendar.MINUTE);
int second = c.get(Calendar.SECOND);
Date date = c.getTime(); //Date和Calendar类互转
Long time = c.getTimeInMillis(); //获取当前毫秒数
//数学函数
Math.abs(a); // java.lang包，求绝对值
Math.pow(a); //指数运算
Math.random(); //产生从0到1间的随机数
Math.round(a); //求近似
Math.floor(); //返回小于参数的最大整数
Math.ceil(); //返回大于参数的最小整数
//集合
//容器类
Collection接口，子接口有Set，List，Queue，实现类有ArrayList, LinkedList, HashSet
Map接口，实现类有HashMap
---------
ArrayList<String> list = new ArrayList<String>(); //定义ArrayList容器，ArrayList是List接口的一个实现类，List是Collection的子接口
list.add(s); //增加元素
list.add(n, s); //在位置n上插入元素
list.addAll(Array.asList(array)); //将数组转换为list并添加到list中
list.addAll(n, Array.asList(array)); //插入到指定位置
list.remove(s); //删除指定元素或指定位置元素
list.removeAll(Array.asList(array)); //删除list中指定的元素集合
list.set(n, s); //修改n位置的元素为s
list.size(); //返回大小
Iterator it = list.iterator(); //获取list的迭代器
it.hasNext(); //判断迭代器是否有下一个元素
it.Next(); //利用迭代器获取下一个元素
//HashMap散列表
HashMap<Integer, String> coinnames = new HashMap<Integer, String>();
coinnames.put(1, "penny"); //放进键值对
coinnames.get(1); //返回键1对应的值
coinnames.containsKey(1); //是否包含某键
coinnames.keySet(); //返回键的集合
//图形界面包
import javax.swing.JFrame; //图形窗口
import javax.swing.JPanel; //图形面板
import javax.swing.JButton; //图形按钮
import java.awt.Color; //颜色设置
import java.awt.Graphics; //绘制图像
import java.awt.BorderLayout; //组件布局管理
import java.awt.event.ActionEvent; //事件处理
import java.awt.event.ActionListener; //事件监听
import javax.swing.JScrollPane; //滚动面板
import javax.swing.JTable; //图形表格
import javax.swing.table.TableModel; //表格的数据模型接口
//图片格式转换、改变大小
package com.qyluo.tmall.utils;import javax.imageio.ImageIO;import java.awt.*;import java.awt.image.*;import java.io.File;import java.io.IOException;/*** Created by qy_lu on 2017/5/10.*/public class ImageUtil {public static BufferedImage change2jpg(File f) {try {java.awt.Image i = Toolkit.getDefaultToolkit().createImage(f.getAbsolutePath());PixelGrabber pg = new PixelGrabber(i, 0, 0, -1, -1, true);pg.grabPixels();int width = pg.getWidth(), height = pg.getHeight();final int[] RGB_MASKS = { 0xFF0000, 0xFF00, 0xFF };final ColorModel RGB_OPAQUE = new DirectColorModel(32, RGB_MASKS[0], RGB_MASKS[1], RGB_MASKS[2]);DataBuffer buffer = new DataBufferInt((int[]) pg.getPixels(), pg.getWidth() * pg.getHeight());WritableRaster raster = Raster.createPackedRaster(buffer, width, height, width, RGB_MASKS, null);BufferedImage img = new BufferedImage(RGB_OPAQUE, raster, false, null);return img;} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();return null;}}public static void resizeImage(File srcFile, int width,int height, File destFile) {try {Image i = ImageIO.read(srcFile);i = resizeImage(i, width, height);ImageIO.write((RenderedImage) i, "jpg", destFile);} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}public static Image resizeImage(Image srcImage, int width, int height) {try {BufferedImage buffImg = null;buffImg = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);buffImg.getGraphics().drawImage(srcImage.getScaledInstance(width, height, Image.SCALE_SMOOTH), 0, 0, null);return buffImg;} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}return null;}}
//上传文件解析
相关包
import org.apache.commons.fileupload.FileItem;import org.apache.commons.fileupload.disk.DiskFileItemFactory;import org.apache.commons.fileupload.servlet.ServletFileUpload;
public InputStream parseUpload(HttpServletRequest request, Map<String, String> params) {InputStream is = null;try {DiskFileItemFactory factory = new DiskFileItemFactory();ServletFileUpload upload = new ServletFileUpload(factory);factory.setSizeThreshold(1024 * 10240);List items = upload.parseRequest(request);Iterator iterator = items.iterator();while (iterator.hasNext()) {FileItem item = (FileItem) iterator.next();if (!item.isFormField()) {is = item.getInputStream();} else {String paramName = item.getFieldName();String paramValue = item.getString();paramValue = new String(paramValue.getBytes("ISO-8859-1"), "UTF-8");params.put(paramName, paramValue);}}} catch (Exception e) {e.printStackTrace();}return is;}