double d = Math.random();
float f= (float) (5+d);
System.out.println(d);
System.out.println(f);
结果：
0.8689445607363707
5.8689446

double d = Math.random();
float f= (float) (5+d);
System.out.println(d);
System.out.println(f);
结果：
0.8689445607363707
5.8689446