Before Java 1.7, only this one is permitted:

ArrayList<String> a = new ArrayList<String>();

And in 1.7, this is added, which is the same but shorter: (all programmers are lazy)

ArrayList<String> a = new ArrayList<>();

在Java 1.7，只有这一个是允许的：

ArrayList<String> a = new ArrayList<String>();

在1.7，这是说，这是相同的但较短的：（所有的程序员都懒）

ArrayList<String> a = new ArrayList<>();