replace与replaceAll替换字符

public void testString(){
        String str="wel2come3Souhe0";
        System.out.println(str.replace("e","E"));
        System.out.println(str.replace('e','E'));
        System.out.println(str.replaceAll("\\d","A"));
        System.out.println(str.replaceAll("3","9"));
    }