Java不打印一致地加倍[duplicate]

double a = 0.1;
double b = 0.2;
System.out.println(a);
System.out.println(b);
System.out.println(a + b);

0.1
0.2
0.30000000000000004

我所期望的;

0.10000000000000001
0.20000000000000003
0.30000000000000004

编辑: 这些操作之间的区别是什么;

double a = 0.3;
double b = 0.1 + 0.2;
System.out.println(a);   //0.3
System.out.println(b);   //0.300000000000004