jdk7新特性一

public static void main(String[] args) {
String aa = null;
int a = 1_2;//整形常量支持下划线
try {
boolean f=aa.equals("");
a = Integer.parseInt(aa);
System.out.println(a);
} catch (NumberFormatException|NullPointerException e) {//多异常的写法
e.printStackTrace();
}
}

String s = "test";

switch (s) {

case "test" :

System.out.println("test");

case "test1" :

System.out.println("test1");

break ;

default :

System.out.println("break");

break ;

}

Map<Integer, Map<String , String >> users=new HashMap<Integer, Map<String , String >>();
Map<Integer, Map<String , String >> users1=new HashMap<>();