java声明方法抛出的异常-蒲公英云

java声明方法抛出的异常

TestExceptions.java

import java.io.*;
//异常
public class TestExceptions {
    public static void main(String[] args) {
    }
    void f() {//throws FileNotFoundException , IOException 
        FileInputStream in = new FileInputStream("myfile.txt");
        int b;
        b = in.read();
        while (b != -1) {
            System.out.print((char) b);
            b = in.read();
        }
    }
}

抛出异常

F:\java>javac TestExceptions.java
TestExceptions.java:10: 错误: 未报告的异常错误FileNotFoundException; 必须对其进行捕获或声明以便抛出
                FileInputStream in = new FileInputStream("myfile.txt");
                                     ^
TestExceptions.java:12: 错误: 未报告的异常错误IOException; 必须对其进行捕获或声明以便抛出
                b = in.read();
                           ^
TestExceptions.java:15: 错误: 未报告的异常错误IOException; 必须对其进行捕获或声明以便抛出
                        b = in.read();
                                   ^
3 个错误
F:\java>

给方法抛出异常

import java.io.*;
//异常
public class TestExceptions {
    public static void main(String[] args) {
    }
    //throwsthrows FileNotFoundException , IOException
    void f() throws FileNotFoundException , IOException {
        FileInputStream in = new FileInputStream("myfile.txt");
        int b;
        b = in.read();
        while (b != -1) {
            System.out.print((char) b);
            b = in.read();
        }
    }
}

编译没有报异常

F:\java>javac TestExceptions.java
F:\java>
import java.io.*;
//异常
public class TestExceptions {
    public static void main(String[] args) {
    }
    //throwsthrows FileNotFoundException , IOException
    void f() throws FileNotFoundException , IOException {
        FileInputStream in = new FileInputStream("myfile.txt");
        int b;
        b = in.read();
        while (b != -1) {
            System.out.print((char) b);
            b = in.read();
        }
    }
    //throws IOException
    void f2() throws IOException {
                //捕捉f()方法中可能出现的异常
        try {
            f();
        } catch (FileNotFoundException e) {
            System.out.println(e.getMessage());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
import java.io.*;
//异常
public class TestExceptions {
    public static void main(String[] args) /*throws Exception*/ {
        try {
            TestExceptions te = new TestExceptions();
            te.f2();
        } catch(IOException e) {
            e.printStackTrace();
        }
    }
    //throwsthrows FileNotFoundException , IOException
    void f() throws FileNotFoundException , IOException {
        FileInputStream in = new FileInputStream("myfile.txt");
        int b;
        b = in.read();
        while (b != -1) {
            System.out.print((char) b);
            b = in.read();
        }
    }
    void f2() throws IOException {
        /*
        方法一：
        //捕捉f()方法中可能出现的异常
        try {
            f();
        } catch (FileNotFoundException e) {
            System.out.println(e.getMessage());
        } catch (IOException e) {
            e.printStackTrace();
        }
        */
        /*
            方法二：
            在f2() 方法后抛出异常f2() throws IOException
        */
        f();
    }
}