Assertion 用法

import java.util.Scanner;

public class Demo {
    public static void main(String[] args){
    
        Scanner scanner = new Scanner(System.in);
        System.out.print("Please input positive number:");
        int input = scanner.nextInt();
        if (input > 0){
            System.out.println("Number: " + input);
        } else {
            assert (input > 0): "執行有誤....";
            System.out.println("Error : " + input);
        }
    }
}

Java 例外處理--AutoCloseable

有 catch 敘述：

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

public class OpenFileDemo{
  public static void main(String[] args){
    System.out.println("About to open a file...");
    
    try (InputStream in = new FileInputStream("hello.txt")){
      System.out.println("File is opened..");
      int data = in.read();
    } catch (FileNotFoundException e){
        System.out.println(e.getMessage());
    } catch (IOException e){
        System.out.println(e.getMessage());
    }
  }
}

沒有 catch 敘述(利用 throws，丟給上頭去傷腦筋...)

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

public class ThrowDemo {
    public static void main(String[] args){
        try {    
            int data = readByteFromFile();
        } catch (IOException ex) {
            System.out.println(ex.getMessage());
        }
    }

    private static int readByteFromFile() throws FileNotFoundException, IOException {
        try(InputStream in = new FileInputStream("a.txt")){
            System.out.println("File is opening...");
            return in.read();
        }
    }
}

Java 例外處理

Java 例外處理(基本處理方式)：

import java.util.Scanner;

public class ErrorDemo{

 public static void main(String[] args){
 
  int input = 0;
  Scanner scanner = new Scanner(System.in);
  System.out.print("請輸入一個整數：");
  try{
   input = scanner.nextInt();
  } catch (Exception e){
   System.out.println("請輸入整數！");
  }
 }
}

使用 throws & throw ：

public class TestArray{

 int [] intArray;
    public TestArray(int size){
  intArray = new int[size];
 }
 
 public void addElement(int index, int value) throws RuntimeException{
  intArray[index] = value;
  throw new ArrayIndexOutOfBoundsException();
 }
}

public class ExceptionDemo{

 public static void main(String[] args){
 
  TestArray myTestArray = new TestArray(5);
  try {
   myTestArray.addElement(5, 23);
  } catch (RuntimeException e){
   System.out.println("超出陣列大小！");
  }
 }
}

Multi-Exception 的用法：

import java.io.*;

public class MultiExceptionDemo{

 public static void main(String[] args){
 
  try{
   createFile();
  } catch (IOException ex1){
   System.out.println(ex1);
  } catch (IllegalArgumentException ex2){
   System.out.println(ex2);
  } catch (Exception ex3){
   System.out.println(ex3);
  }
 }
 
 public static void createFile() throws IOException{
  File test = new File("C://workspace//test.txt");
  File temp1 = test.createTempFile("te123",null,test);
  System.out.println("Temp filename is " + temp1.getPath());
  int[] myInt = new int[5];
  myInt[5] = 25;
 }
}