Java语言程序设计

*定义方法：

修饰符   返回值类型   方法名（参数列表）{

//方法体;

}

对于：public static int max(int num1,int num2){

...

}这个方法，public static作为修饰符，为静态修饰符；int为说明该方法的返回值是一个int型数据，这个方法包含两个int型形式参数。

主程序main()也是一种方法，它是由Java虚拟机进行调用的。

*可以看出Java中的方法几乎就等同于C语言中的函数，并且与C中在参数传递上也都是：传递的只是实参的值，而非实参本身。

*重载方法：Java中一个类里面可以有多个同名方法，但其各自的参数表不同；编译器会根据情况选择最匹配的方法。但多个方法匹配度相同时候会产生编译错误，称为歧义调用。

*变量的作用域

是指变量可在程序中引用的范围。方法中的变量称为局部变量。局部变量作用域是从其声明开始，到包含该变量声明的块结束。局部变量在使用之前要先进行声明。基于此，可以在一个方法的不同代码块里声明同名的局部变量。

*输入年份和月份，显示该月日历

[java] view plaincopyprint?

1. import java.util.Scanner;  
2. public class C0501 {  
3.     public static void main(String[] args){  
4.         Scanner input=new Scanner(System.in);  
5.         System.out.print("请输入年份：");  
6.         int year=input.nextInt();  
7.         System.out.print("请输入月份：");  
8.         int month=input.nextInt();  
9.         int monthDays=31;  
10.         if(month%2==0&&month!=8)  
11.             monthDays=30;  
12.         if(month==2)  
13.             monthDays=28;  
14.         if(leapYear(year)==1&&month==2)  
15.             monthDays=29;  
16.         int countLeapYear=0;  
17.         for(int i=1800;i<year;i++){  
18.             if(leapYear(i)==1)  
19.                 countLeapYear++;  
20.         }  
21.         int dateCount=(year-1800)*365+countLeapYear;  
22.         String ms1="Jan";  
23.         switch(month){  
24.         case 2:dateCount+=31;ms1="Feb";break;  
25.         case 3:dateCount+=59;ms1="Mar";break;  
26.         case 4:dateCount+=90;ms1="Apr";break;  
27.         case 5:dateCount+=120;ms1="May";break;  
28.         case 6:dateCount+=151;ms1="June";break;  
29.         case 7:dateCount+=181;ms1="July";break;  
30.         case 8:dateCount+=212;ms1="Aug";break;  
31.         case 9:dateCount+=243;ms1="Sep";break;  
32.         case 10:dateCount+=273;ms1="Oct";break;  
33.         case 11:dateCount+=304;ms1="Nov";break;  
34.         case 12:dateCount+=334;ms1="Dec";break;  
35.         default:break;  
36.         }  
37.         if(month>1&&(leapYear(year)==1))  
38.             dateCount++;  
39.         int n=(dateCount%7+3)%7;  
40.         int pcount=0;  
41.         System.out.printf("             %s  %d             \n",ms1,year);  
42.         System.out.println("-----------------------------------");  
43.         System.out.println("  Sun  Mon  Tue  Wed  Thu  Fri  Sat");  
44.         for(int i=1;i<=n;i++){  
45.             System.out.print("     ");  
46.             pcount++;  
47.         }  
48.         for(int i=0;i<monthDays;i++){  
49.             if(pcount%7==0)  
50.                 System.out.printf("\n");  
51.             System.out.printf("%5d",i+1);  
52.             pcount++;  
53.         }         
54.     }  
55.     public static int leapYear(int n){  
56.         if(n%4==0&&(n%100!=0))  
57.             return 1;  
58.         else if(n%400==0)  
59.             return 1;  
60.         else   
61.             return 0;  
62.     }  
63.   
64. }  

编程练习：

5.26，显示前100个回文素数

[java] view plaincopyprint?

1. public class C05T26 {  
2.     public static void main(String[] args){  
3.         int counter=0;  
4.         int i=2;  
5.         while(counter<100){  
6.             if(judgeHuiwen(i)&&judgePrime(i)){  
7.                 counter++;  
8.                 System.out.printf("%8d",i);  
9.                 if(counter%10==0)  
10.                     System.out.printf("\n");  
11.             }  
12.             i++;  
13.         }  
14.     }  
15.     public static boolean judgeHuiwen(int n){  
16.         int k=n;  
17.         int rNum=0,remain;  
18.         while(k!=0){  
19.             remain=k%10;  
20.             rNum=rNum*10+remain;              
21.             k=k/10;           
22.         }  
23.         if(rNum==n)  
24.             return true;  
25.         else  
26.             return false;  
27.     }  
28.     public static boolean judgePrime(int n){  
29.         int i;  
30.         if(n==0||n==1)  
31.             return false;  
32.         for(i=2;i<=n;i++){  
33.             if(n%i==0)  
34.                 break;  
35.         }  
36.         if(i==n)  
37.             return true;  
38.         else  
39.             return false;             
40.     }  
41.   
42. }  

5.33调用System.currentTimeMillis()显示当前日期和时间。

[java] view plaincopyprint?

1. import javax.swing.JOptionPane;  
2. public class C05T33 {  
3.     public static void main(String[] args){  
4.         long totalms=System.currentTimeMillis();  
5.         long year=cYear(totalms);  
6.         String month=cMonth(totalms);  
7.         long date=cDate(totalms);  
8.         long hour=cHour(totalms);  
9.         long min=cMin(totalms);  
10.         long sec=cSec(totalms);  
11.         JOptionPane.showMessageDialog(null,"Current date and" +  
12.                 " time is "+month+" "+date+", "+year+" "+  
13.                 hour+":"+min+":"+sec);  
14.     }  
15.     public static long cYear(long n){  
16.         long x=0;  
17.         long days=n/1000/3600/24;  
18.         long i=1969;  
19.         while(days>=x){  
20.             if(leapYear(i))  
21.                 x+=366;  
22.             else  
23.                 x+=365;  
24.             i++;  
25.         }  
26.         return i;  
27.     }  
28.     public static String cMonth(long n){  
29.         long days=n/1000/3600/24;  
30.         long i;  
31.         for(i=1970;i<cYear(n);i++){  
32.             days=days-365;  
33.             if(leapYear(i))  
34.                 days--;  
35.         }  
36.         String x="";  
37.         if(leapYear(cYear(n))){  
38.             if(days<=31)  
39.                 x="Jan";  
40.             if(days<=60&&days>31)  
41.                 x="Feb";  
42.             if(days<=91&&days>60)  
43.                 x="Mar";  
44.             if(days<=121&&days>91)  
45.                 x="Apr";  
46.             if(days<=152&&days>121)  
47.                 x="May";  
48.             if(days<=182&&days>152)  
49.                 x="Jun";  
50.             if(days<=213&&days>182)  
51.                 x="Jul";  
52.             if(days<=244&&days>213)  
53.                 x="Aug";  
54.             if(days<=274&&days>244)  
55.                 x="Sep";  
56.             if(days<=304&&days>274)  
57.                 x="Oct";  
58.             if(days<=335&&days>304)  
59.                 x="Nov";  
60.             if(days<=366&&days>335)  
61.                 x="Dec";  
62.         }  
63.         else{  
64.             if(days<=31)  
65.                 x="Jan";  
66.             if(days<=59&&days>31)  
67.                 x="Feb";  
68.             if(days<=90&&days>59)  
69.                 x="Mar";  
70.             if(days<=120&&days>90)  
71.                 x="Apr";  
72.             if(days<=151&&days>120)  
73.                 x="May";  
74.             if(days<=181&&days>151)  
75.                 x="Jun";  
76.             if(days<=212&&days>181)  
77.                 x="Jul";  
78.             if(days<=243&&days>212)  
79.                 x="Aug";  
80.             if(days<=273&&days>243)  
81.                 x="Sep";  
82.             if(days<=303&&days>273)  
83.                 x="Oct";  
84.             if(days<=334&&days>303)  
85.                 x="Nov";  
86.             if(days<=365&&days>334)  
87.                 x="Dec";              
88.         }  
89.         return x;  
90.     }  
91.     public static long cDate(long n){  
92.         long days=n/1000/3600/24;  
93.         long i,x=0;  
94.         for(i=1970;i<cYear(n);i++){  
95.             days=days-365;  
96.             if(leapYear(i))  
97.                 days--;  
98.         }  
99.         if(leapYear(cYear(n))){  
100.             if(days<=31)  
101.                 x=31-days;  
102.             if(days<=60&&days>31)  
103.                 x=60-days;  
104.             if(days<=91&&days>60)  
105.                 x=91-days;  
106.             if(days<=121&&days>91)  
107.                 x=121-days;  
108.             if(days<=152&&days>121)  
109.                 x=152-days;  
110.             if(days<=182&&days>152)  
111.                 x=182-days;  
112.             if(days<=213&&days>182)  
113.                 x=213-days;  
114.             if(days<=244&&days>213)  
115.                 x=244-days;  
116.             if(days<=274&&days>244)  
117.                 x=274-days;  
118.             if(days<=304&&days>274)  
119.                 x=304-days;  
120.             if(days<=335&&days>304)  
121.                 x=335-days;  
122.             if(days<=366&&days>335)  
123.                 x=366-days;  
124.         }  
125.         else{  
126.             if(days<=31)  
127.                 x=31-days;  
128.             if(days<=59&&days>31)  
129.                 x=59-days;  
130.             if(days<=90&&days>59)  
131.                 x=90-days;  
132.             if(days<=120&&days>90)  
133.                 x=120-days;  
134.             if(days<=151&&days>120)  
135.                 x=151-days;  
136.             if(days<=181&&days>151)  
137.                 x=181-days;  
138.             if(days<=212&&days>181)  
139.                 x=212-days;  
140.             if(days<=243&&days>212)  
141.                 x=243-days;  
142.             if(days<=273&&days>243)  
143.                 x=273-days;  
144.             if(days<=303&&days>273)  
145.                 x=303-days;  
146.             if(days<=334&&days>303)  
147.                 x=334-days;  
148.             if(days<=365&&days>334)  
149.                 x=365-days;           
150.         }  
151.         return x;  
152.     }  
153.     public static long cHour(long n){  
154.         long hours=(n/1000/3600+8)%24;  
155.         return hours;  
156.     }  
157.     public static long cMin(long n){  
158.         long hours=n/1000/60%60;  
159.         return hours;  
160.     }  
161.     public static long cSec(long n){  
162.         long hours=n/1000%60;  
163.         return hours;  
164.     }  
165.     public static boolean leapYear(long n){  
166.         if(n%4==0&&(n%100!=0))  
167.             return true;  
168.         else if(n%400==0)  
169.             return true;  
170.         else   
171.             return false;  
172.     }  
173.   
174. }