Java学习笔记（四）

30、31_异常

1.异常的各种使用：

class User {
	private int age;

	public void setage(int age) throws Exception {
		if (age < 0) {
			/*
			 * RuntimeException e = new RuntimeException("年龄不能为负数"); 
			 * throw e;
			 */
			Exception e = new Exception("年龄不能为负数");
			throw e;
		}
		this.age = age;
	}
}

public class Test {
	public static void main(String[] args) {
		User user = new User();
		
		try {
			user.setage(-10);
		} catch (Exception e) {
			System.out.println(e);
		}
		
		finally {
			System.out.println("clean");  //无论是否发生异常,都执行
		}
	}
}

32、33、34_IO流

1.IO分类方法：

第一种分法：
输入流、输出流
第二种分法：
字节流、字符流
第三种分法：
节点流、处理流

2.字节流的使用：

FileInputStream 
FileOutputStream
byte buffer[]

import java.io.*;

public class Test {
	public static void main(String[] args) {
		FileInputStream fin = null;
		FileOutputStream fout = null;
		try {
			fin = new FileInputStream("c:/from.txt");
			fout = new FileOutputStream("c:/out.txt");

			byte[] buffer = new byte[100];
			int temp = fin.read(buffer, 0, buffer.length); // read()返回读取的字节（byte）数
			fout.write(buffer, 0, temp);

			String str = new String(buffer);
			System.out.println(str.trim()); // 删除字符串首尾空格
		} catch (Exception e) {
			System.out.println(e);
		}
	}
}

大文件：

import java.io.*;

public class Test {
	public static void main(String[] args) {
		FileInputStream fin = null;
		FileOutputStream fout = null;
		try {
			fin = new FileInputStream("c:/from.txt");
			fout = new FileOutputStream("c:/out.txt");

			byte[] buffer = new byte[1024];

			while (true) {
				int temp = fin.read(buffer, 0, buffer.length);
				if (temp == -1) {
					break;
				}
				fout.write(buffer, 0, temp);
			}
		} catch (Exception e) {
			System.out.println(e);
		} finally {
			try {
				fin.close();
				fout.close();
			} catch (Exception e) {
				System.out.println(e);
			}
		}
	}
}

3.字符流的使用：

同字节流相似

FileReader
FilrWriter
char buffer[]

4.处理流：

import java.io.*;

public class Test {
	public static void main(String[] args) {
		FileReader fileReader = null;
		BufferedReader bufReader = null;
		try {
			fileReader = new FileReader("c:/from1.txt");
			bufReader = new BufferedReader(fileReader);
			String line = null;
			while (true) {
				line = bufReader.readLine();
				if (line == null) {
					break;
				}
				System.out.println(line);
			}
		} catch (Exception e) {
			System.out.println(e);
		} finally {
			try {
				fileReader.close();
				bufReader.close();
			} catch (Exception e) {
				System.out.println(e);
			}
		}
	}
}

5.装饰者模式：

interface Worker {
	public void dosomework();
}

class AWorker implements Worker {
	private Worker worker;

	public AWorker() {
		
	}
	
	public AWorker(Worker worker) {
		this.worker = worker;
	}

	public void dosomework() {
		System.out.println("教授好");
		worker.dosomework();
	}
}

class Carpenter implements Worker {
	public void dosomework() {
		System.out.println("修门窗");
	}
}

class Plumber implements Worker {
	public void dosomework() {
		System.out.println("修水管");
	}
}

import java.io.*;

public class Test {
	public static void main(String[] args) {
		Plumber plu = new Plumber();
		Carpenter cp = new Carpenter();
		AWorker Aw = new AWorker(plu);
		AWorker Aw2 = new AWorker(cp);
		
		Aw.dosomework();
		Aw2.dosomework();
	}
}