数学中，没有办法用十进制来精确表达1/3.
同样的，计算机中，没有办法用二进制表示0.1
比如：python中，java中 都是一样的。
>>> a=6.0
>>> b=4.9
>>> a-b
1.0999999999999996
>>> x=3.0
>>> y=2.9
>>> x-y
0.10000000000000009
>>> (x-y)>0.1
True
>>> (x-y)==0.1
False
>>>
在上述代码中： a-b 的值会无限接近于1.1。 x-y 的值会无限接近0.1。
1 package day02;
2
3 import java.util.Scanner;
4
5 public class inp_demo {
6
7 public static void main(String[] args) {
8 // TODO Auto-generated method stub
9 Scanner scanner=new Scanner(System.in);
10 String name=scanner.next();
11 System.out.println(name);
12
13 }
14
15 }
数据类型的练习：
1 package day02;
2
3 import java.util.Scanner;
4
5 public class inp_demo {
6
7 public static void main(String[] args) {
8 // TODO Auto-generated method stub
9 // Scanner scanner=new Scanner(System.in);
10 // String name=scanner.next();
11 // System.out.println(name);
12 int a=250;
13 //int b=100000000000;
14 System.out.println(5/2);
15 System.out.println(2/5);
16 int c=2147483647;
17 System.out.println(c+1);
18
19 //long d=10000000000;
20 long e=10000000000L;
21 long f=1000000000*2*10L;
22 System.out.println("f:"+f);
23 long g=1000000000*3*10L;
24 System.out.println("g>>>"+g);
25 long h=1000000000L*3*10;
26 System.out.println("e>>>"+h);
27 long i;
28 i=System.currentTimeMillis();
29 System.out.println("time:"+i);
30
31
32 float j=3.14f;
33 float k,l;
34 k=6.0f;
35 l=4.9f;
36 System.out.println(k-l);
37
38 }
39
40 }
结果：
2
0
-2147483648
f:20000000000
g>>>-12949672960
e>>>30000000000
time:1535892324164
1.0999999
1 package day02;
2
3 import java.util.Scanner;
4
5 public class inp_demo {
6
7 public static void main(String[] args) {
8 // TODO Auto-generated method stub
9
10 // //布尔类型，占一个字节。
11 // boolean b1=true;
12 // boolean b2=false;
13 //字符类型，占有两个字节 java的字符编码表是unicode
14 char o3='m';
15 char o4=' ';
16 char o5=65515;//0~65535
17 System.out.println(o5);
18 char o='中';
19 System.out.println(o);
20
21 char o1='\u4e2d';
22 System.out.println(o1);
23
24 char o2=65;
25 System.out.println(o2);
26
27 System.out.println("(2+2):"+(2+2));
28 System.out.println('2'+'2');
29
30 System.out.println("char2》\t》》\n》"+'2');
31
32
33
34
35
36
37
38
39
40
41 // Scanner scanner=new Scanner(System.in);
42 // String name=scanner.next();
43 // System.out.println(name);
44 /*
45 int a=250;
46 //int b=100000000000;
47 System.out.println(5/2);
48 System.out.println(2/5);
49 int c=2147483647;
50 System.out.println(c+1);
51
52 //long d=10000000000;
53 long e=10000000000L;
54 long f=1000000000*2*10L;
55 System.out.println("f:"+f);
56 long g=1000000000*3*10L;
57 System.out.println("g>>>"+g);
58 long h=1000000000L*3*10;
59 System.out.println("e>>>"+h);
60 long i;
61 i=System.currentTimeMillis();
62 System.out.println("time:"+i);
63
64
65 float j=3.14f;
66 float k,l;
67 k=6.0f;
68 l=4.9f;
69 System.out.println(k-l);
70 */
71
72 }
73
74 }
练习
//类型强制转换.从小到大，系统自动转换，从大到小，需要强制转换，强转可能会导致进度丢失，或是溢出
int age=20;
long age_l=(long)age;
System.out.println(age_l);
long d=5;//int type into long type
double e=5;//int type into double type
double f=3.14f;//float type into double type
double h=25.987;
int i=(int)h;
System.out.println(i);//print>>> 25
