String的几种初始化方法的区别

String a;

String aa = "";

String aaa = "123";

String b = new String();

String bb = new String("");

String bbb = new String("123");

String c = null;

?

System.out.println(aa == bb);????????// false

System.out.println(aa.equals(bb));????// true

System.out.println(aa.equals(b));????// true

System.out.println(b == bb);????????// false

System.out.println(bb.equals(b));????// true

System.out.println(c);????????????????// null