orElse orElseGet orElseThrow

當ofNullable包含的對象值不存在時候，orElse都會走自己包含的方法，orElseGet則會智能判斷。

    /**
     * orElse執行----
     * orElseGet執行----
     * ycw---------ycw
     */
    @Test
    public void myOPtions1(){
        Map<String,String> obj = null;
        String name1 = Optional.ofNullable(obj).map(x -> x.get("name")).orElse(get("orElse"));
        String name2 = Optional.ofNullable(obj).map(x -> x.get("name")).orElseGet(()->get("orElseGet"));
        System.out.println(name1+"---------"+name2);
    }

    /**
     * orElse執行----
     * wk---------wk
     * 總結：當ofNullable包含的對象值不存在時候，orElse都會走自己包含的方法，orElseGet則會智能判斷。
     */
    @Test
    public void myOPtions2(){
        Map<String,String> obj = new HashMap<String,String>(){{
            put("name","wk");
        }};
        String name1 = Optional.ofNullable(obj).map(x -> x.get("name")).orElse(get("orElse"));
        String name2 = Optional.ofNullable(obj).map(x -> x.get("name")).orElseGet(()->get("orElseGet"));
        System.out.println(name1+"---------"+name2);
    }
    @Test
    public void myOPtions3() throws DemoException {
        Map<String,String> obj = null;
        String name1 = Optional.ofNullable(obj).map(x -> x.get("name")).orElse(get("orElse"));
        String name2 = Optional.ofNullable(obj).map(x -> x.get("name")).orElseGet(()->get("orElseGet"));
        String name3 = Optional.ofNullable(obj).map(x -> x.get("name")).orElseThrow(()->new DemoException("我是一個錯誤"));
        System.out.println(name1+"---------"+name2+"----------"+name3);
    }
    private String get(String arg) {
        System.out.println(arg+"執行----");
        return "ycw";
    }
    class DemoException extends Throwable {


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

    }