Java筆記 - Exception Catch & Throw

如果function內自己會拋出Exception,
或者再深一層有拋出Exception但你沒有執行catch區塊, 那麼在compile階段就會報error

一個簡單的範例程式如下:

public class throwTest {

    private static void throwTestLayer1() throws Exception {
        System.out.println("throwTestLayer1: throw Exception +++");
        throw new Exception("throwTestLayer1: throwExcept test");
    }

    private static void throwTestLayer2() throws Exception {
        System.out.println("throwTestLayer2: calling throwTestLayer1 +++");
        throwTestLayer1();
        System.out.println("throwTestLayer2: calling throwTestLayer1 ---");
    }

    private static void throwTestLayer2Catch() throws Exception {
        try {
            System.out.println("throwTestLayer2Catch: calling throwTestLayer1 +++");
            throwTestLayer1();
            System.out.println("throwTestLayer2Catch: calling throwTestLayer1 ---");
        } catch (Exception e) {
            System.out.println("throwTestLayer2Catch: Catch throwTestLayer1");
            e.printStackTrace();
            //throw e;
        }
    }

    public static void main(String[] argv) {

        // 單層的 throw
        System.out.println("=============================================================");
        try {
            System.out.println("main: Calling throwTestLayer1 +++");
            throwTestLayer1();
            System.out.println("main: Calling throwTestLayer1 ---");
        } catch (Exception e) {
            System.out.println("main: Catch throwTestLayer1");
            e.printStackTrace();
        }
        System.out.println("=============================================================");

        // 這個 throwTestLayer2 並沒有去執行 try/catch, 他必須宣告 throws
System.out.println("=============================================================");
        try {
            System.out.println("main: Calling throwTestLayer2 +++");
            throwTestLayer2();
            System.out.println("main: Calling throwTestLayer2 ---");
        } catch (Exception e) {
            System.out.println("main: Catch throwTestLayer2");
            e.printStackTrace();
        }
        System.out.println("=============================================================");

        // 這個 throwTestLayer2Catch 將會執行 catch, 如果它不再 throw, 這時候 main 是接不到的
System.out.println("=============================================================");
        try {
            System.out.println("main: Calling throwTestLayer2Catch +++");
            throwTestLayer2Catch();
            System.out.println("main: Calling throwTestLayer2Catch ---");
        } catch (Exception e) {
            System.out.println("main: Catch throwTestLayer2Catch");
            e.printStackTrace();
        }
        System.out.println("=============================================================");
    }
}