java-测试Try-catch-finally

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

class Test425{
    public static void main(String[] args) throws ParseException {
//        test01();
//        test2();
//        test3();
        System.out.println(test4());
    }
    //测试try  catch  finally
    public static void test01(){
        FileReader fileReader=null;
        try {
            fileReader = new FileReader("d:/a.txt");
            try {
                char  c1 = (char)fileReader.read();
                char  c2 = (char)fileReader.read();
                System.out.println("文件内容为："+c1+c2);
            } catch (IOException e) {
                e.printStackTrace();
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }finally {
            if (fileReader!=null){
                try {
                    fileReader.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    //测试throws，声明式抛出异常
    public static void test2() throws ParseException{
        DateFormat df  = new SimpleDateFormat("yyyy-MM-dd");
        String str = "2049-10-1";
        Date date = df.parse(str);
        System.out.println(date);
    }
    /*
    “try with resourse”即：try（读取文件的对象），自动关闭AutoCloseable类接口
    将Try catch finally简化try catch
    本质都一样，知识编译器自动帮你处理
     */
    public static void test3(){
        //因为他实现了AutoCloseable接口，所以会自动转
        try (FileReader fr = new FileReader("d:/a.txt")){
            char  c1 = (char)fr.read();
            char  c2 = (char)fr.read();
            System.out.println("文件内容为："+c1+c2);
        }catch(Exception e){
            e.getMessage();
        }
    }

    public static int test4(){
        int a = 10;
        System.out.println("step1");
        try {
            System.out.println("step2");

            a = 20;
            return a;
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            a=40;
            System.out.println("step3");
            return a;
        }
    }
}