markdown todo，java，number

Posted 2021-05-05

## Read Source Code Of Format related Classes
### Why NumberFormat need a local as it's paramater
当输出数字时， 各国的 Format 是不一样的， 比如货币符号， 美国是$, 欧洲是€。大数字时， 间隔也是不一样的， 所以需要这个locale 做客制化
```Java
    public static void main(String[] args) {
        float test = 1.20f;
        System.out.println("currency ret: " + NumberFormat.getCurrencyInstance().format(test));
        System.out.println("France ret: " + NumberFormat.getCurrencyInstance(Locale.FRANCE).format(test));

        System.out.println("default format: " + NumberFormat.getInstance().format(1000000));
        System.out.println("German ret: " + NumberFormat.getInstance(Locale.GERMAN).format(1000000));

        System.out.println("percent format: " + NumberFormat.getPercentInstance().format(test));
    }

-------
output:
currency ret: $1.20
France ret: 1,20 €
default format: 1,000,000
German ret: 1.000.000
percent format: 120%
```