Tou Ge (educoder) Chapter 7 Java Object-Oriented Exception Class and File Class

Table of contents

Java Object Orientation - Exceptions in Java

Level 1: Exception handling mechanism in Java

Level 2: Catching exceptions 

Level 3: Throw an exception

Level 4: Custom exception

Java object-oriented - file class

Level 1: Create File

Level 2: Common operations on files

Level 3: File Viewer

Level 4: Picture Viewer

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Java Object Orientation - Exceptions in Java

Level 1: Exception handling mechanism in Java

 

Level 2: Catching exceptions 

package step2;

import java.util.Scanner;

public class Task {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int num1 = sc.nextInt();
		int num2 = sc.nextInt();
		/********* Begin *********/
		try{
System.out.println(num1/num2);
		}catch(ArithmeticException e){
			System.out.println("除数不能为0");
		}
		
		
		
		
		/********* End *********/
	}

}

Level 3: Throw an exception

package step3;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

public class Task {
	/********* Begin *********/
	//请在合适的部位添加代码
	public static void main(String[] args) throws FileNotFoundException        {	
		test();
	}
	public static void test()throws FileNotFoundException      {
		File file = new File("abc");
		if(!file.exists()){		//判断文件是否存在
			//文件不存在，则 抛出 文件不存在异常
		throw	 new FileNotFoundException("该文件不存在");
		}else{
			FileInputStream fs = new FileInputStream(file);
		}
	}
	/********* End *********/
}

Level 4: Custom exception

package step4;

import java.util.Scanner;

public class Task {
	/********* Begin *********/
	public static void main(String[] args) throws MyException{
		Scanner sc = new Scanner(System.in);
		String username = sc.next();
		if(username.length()<3){
			throw new MyException("用户名小于三位Exception");
		}else System.out.println("用户名格式正确");

		//判断用户名
		
		
	}
}

class MyException extends Exception{
	public MyException(){

	}
	public MyException(String msg){
		super(msg);
	}
}

/********* End *********/

---

Java object-oriented - file class

Level 1: Create File

package step1;

import java.io.File;
import java.io.FileFilter;
import java.io.IOException;
import java.util.Scanner;

public class Task {
	/********* Begin *********/
	public void solution()throws IOException           {
	File file1=new File("src/output/test.txt");
file1.createNewFile();
			File file2=new File("src/output/hello.txt");
			
			
			file2.createNewFile();
		
		
		
		
		
		
		/********* End *********/
	}
}

Level 2: Common operations on files

package step2;

import java.io.File;
import java.io.FileFilter;
import java.io.IOException;
import java.util.Arrays;


public class Task {
	public static void dcFile() throws IOException {
		/********* Begin *********/
	File file1=new File("src/test2");
	    file1.mkdirs();
		File file2=new File("src/output/test2.txt");
		file2.delete();
		File file3=new File("src/test2/helloworld.txt");
		file3.createNewFile();
		File file4=new File("src/test2/step2.txt");
		file4.createNewFile();

		System.out.println("output目录结构为：");
		File[] file5=new File("src/output").listFiles();
		Arrays.sort(file5);
		for(File file:file5){
			System.out.println(file.getName());
		}


		
		System.out.println("test2目录结构为：");
File[] file6=new File("src/test2").listFiles();
		Arrays.sort(file6);
		for(File file:file6){
			System.out.println(file.getName());
		}


		/********* End *********/
	}
}

Level 3: File Viewer

package step3;

import java.io.File;
import java.util.Arrays;

public class Task {
	
	/********** Begin **********/
	String dir="+--";
	String wj="--";
	String level="";
	public void showDirStructure(File file)	{
		if(file.isDirectory()){
			System.out.println(level+dir+file.getName());
			String level1=level;
			level+="  ";
			File[] files=file.listFiles();
			Arrays.sort(files);
			for(File file1:files){
				showDirStructure(file1);
			}
			level=level1;
		}else{
			System.out.println(level+wj+file.getName());
		}





	}
	


	/********** End **********/
}

Level 4: Picture Viewer

package step4;

import java.io.File;
import java.io.FileFilter;
import java.util.Arrays;
public class Task {
	
	/********** Begin **********/
	String dir="+--";
	String wj="--";
	String level="";
    
	public void showDirStructure(File file)	{
		if(file.isDirectory()){
			System.out.println(level+dir+file.getName());
			String level1=level;
			level+="  ";
			File[] files=file.listFiles();
			Arrays.sort(files);
			for(File file1:files){
				showDirStructure(file1);
			}
			level=level1;
		}else{
			String name=file.getName();
			if(name.endsWith("jpg")||name.endsWith("bmp")||name.endsWith("png"))
			System.out.println(level+wj+name);
		
		}






	}
	

	/********** End **********/
}