Java Beginner _java cycle _for loop in simple example

 

Java based portal - loop for circulating a simple example

 

first look for the grammatical structure:

 

  

for(表达式1;表达式2;表达式3){ 
    循环语句 
}

 

 

or more intuitive representation of this:

 

  

for(变量初始化;循环条件;迭代语句){ 
    循环语句 
}

 

 

for loop execution processes are:

 

performed first expression 1, is generally carried variable initialization and then execute the expression 2, namely loop condition to judge, if the result is true, the loop body is executed; circulation After executing body, the Executive expression 3, changing the value of the loop variable, again executing the expression 2; evaluates to true, the loop continues; if the result is false, the loop is terminated, execute the statement following.

 No matter how many times

execution, the expression an executed only once.

 

we give an example, write a little code to achieve the java code 1-100 summation?

 

1 +2 +3 + ...... +100 =?

 

  

package com.student.exam; 
 
/**
*计算1到100的和
*/
public class Summation { 
 
    public static void main(String[] args) { 
        int sum = 0; //声明变量sum存放计算的和，赋初值为0
        for(int i=1;i<=100;i++) 
            sum +=i;//等价于语句sum=sum+score 
        System.out.println("sum="+sum); 
    } 
 
}

 

 

Run Results: sum = 5050

 

for loop suitable for a fixed number of cycles the situation. The number of cycles is not fixed, such as arrays and collections cycle traversal, you can use a foreach loop. foreach loop does not need to know the number of cycles, the later explanation.

 

it another adder using java 1-100 and

 

(1 +100) + (2 +99) + ...... (50 +51) =?

 

  

 1 package com.student.exam; 
 2 /** 
 3  * 使用for循环实现1到100的和 
 4  * 两头相加进行计算 
 5  * (1+100)+(2+99)+(3+98)+... ...+ (50+51) 
 6  */ 
 7 public class  Summation2{ 
 8  
 9     public static void main(String[] args) { 
10         int sum = 0; 
11         for(int i=1,j=100;i<j;i++,j--){ 
12             sum+=i+j; 
13         } 
14         System.out.println("sum= "+sum); 
15     } 
16  
17 }

 

 

Let us realize that the calculation of student achievement for loop code:
assume given a student's homework grades 5, the required output averages

 

  

 1 package com.student.exam; 
 2 /** 
 3  * 使用for 循环 
 4  * 输入学生的5们功课，查询该学生的总成绩和平均分数 
 5  */ 
 6 import java.util.Scanner; 
 7  
 8 public class AverageScores { 
 9     public static void main(String[] args) { 
10         int score;    //声明一个变量，取名为score，用来接收学生的成绩值 
11         int sum= 0;    //声明一个变量，取名sum，用来存储学生的成绩和                 
12         double avg =0.0;    //声明一个double类型的变量，用来接收计算出来的学生的平均分 
13         Scanner sc = new Scanner(System.in);    //获取键盘输入 
14         System.out.println("请输入学生的姓名："); 
15         String name = sc.next();    //将获取的输入赋值给一个String类型的name变量 
16         int i= 0;        //声明一个int类型的变量，赋初始值为0 
17         for(;i<5;i++){    //循环5次录入成绩 
18             System.out.println("请输入5门功课的第"+(i+1)+"门的成绩："); 
19             score = sc.nextInt();    //录入成绩 
20             sum += score;      //等价于语句 sum=sum+score;  
21             System.out.println(name+"的前"+(i+1)+"门功课的成绩和是："+sum); 
22         }     
23         System.out.println(name+"的总成绩是："+sum); 
24         avg = sum/5;    //计算平均成绩 
25         System.out.println(name+"的平均分是："+avg); 
26  
27     } 
28  
29 }

 

 

because this is a fundamental part of Java, are the initial java, so every line of code are given notes, more intuitive feel for beginners, I put one of the English character identifier for to do instead.

 

Note: Although the use of Chinese in Eclipse to run, but in the actual development, it is recommended to use the full English are named.

 

  

 1 package com.student.exam; 
 2     /** 
 3      * 使用for 循环 
 4      * 输入学生的5们功课，查询该学生的总成绩和平均分数 
 5      */ 
 6 import java.util.Scanner; 
 7  
 8 public class 求学生的平均成绩 { 
 9     public static void main(String[] args) { 
10         int 单科成绩; 
11         int 总成绩= 0; 
12         double 平均分 =0; 
13         Scanner 键盘输入 = new Scanner(System.in); 
14         System.out.println("请输入学生的姓名："); 
15         String 学生姓名 = 键盘输入.next(); 
16         int i= 0; 
17         for(;i<5;i++){ 
18             System.out.println("请输入5门功课的第"+(i+1)+"门的成绩："); 
19             单科成绩 = 键盘输入.nextInt(); 
20             总成绩 += 单科成绩; 
21             System.out.println(学生姓名+"的前"+(i+1)+"门功课的成绩和是："+总成绩); 
22         }     
23         System.out.println(学生姓名+"的总成绩是："+总成绩); 
24         平均分 = 总成绩/5; 
25         System.out.println(学生姓名+"的平均分是："+平均分); 
26  
27     } 
28  
29 }

 

 

Finally, we use the java for loop output raster graphics

 

  

 1 package com.student.exam; 
 2  
 3 public class PrintTX { 
 4     public static void main(String[] args) { 
 5         printJX(); 
 6         printPXSBX(); 
 7         printSJX(); 
 8          
 9     } 
10     //打印矩形 
11     private static void printJX(){ 
12         for(int i=1;i<=5;i++){ 
13             for(int j=1;j<=5;j++){ 
14                 System.out.print("*"); 
15             } 
16             System.out.println(); 
17         } 
18     } 
19     //打印平行四边形 
20     private static void printPXSBX(){ 
21         for(int i=1;i<=5;i++){ 
22             for(int k=1;k<=5-i;k++){ 
23                 System.out.print(" "); 
24             } 
25             for(int j=1;j<=5;j++){ 
26                 System.out.print("*"); 
27             } 
28             System.out.println(); 
29         } 
30     } 
31     //打印三角形 
32     private static void printSJX() { 
33         for(int i=1;i<=5;i++){ 
34             for(int k=1;k<=5-i;k++){ 
35                 System.out.print(" "); 
36             } 
37             for(int j=1;j<=2*i-1;j++){ 
38                 System.out.print("*"); 
39             } 
40             System.out.println(); 
41         } 
42          
43     } 
44  
45 }

 

 

results are as follows:
*****
*****
*****
*****
**** *
*****
*****
*****
**** *
*****

 

*
***
*****
*******
*********

 

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