JAVA基础

JAVA基础课程

2017-6-28

1、for语句的执行逻辑

for（表达式1；表达式2；表达式3）{

语句块（循环体）

}

for(int i=1;i<=10;i++){

System.out.print(i);

}

---

public class LoopDemo{

public static void main(String [] args){

int j=0;

for(j++;j++<4;j++);

System.out.println(++j);

}

}

package javaDemo;

public class day1 {

       public static void main(String[] args){

              int a=1,b=0,c=0;

              for(;a<10;a++){

                     for(;b<10;b++){

                            for(;c<10;c++){

                                   System.out.println(a+" "+b+" "+c);

                            }

                     }

              }

       }

       

}

100--109

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2. 课堂作业

（1）.计算1到100之间不能被3整除的数之和

 package work1;

public class work1 {

       public static void main(String[] args){

              int sum=0;

              for(int i=0;i<=100;i++){

                     if(i%3!=0){

                            sum=sum+i;

                     }

              }

              System.out.println(sum);

       }

}

---

（2）.循环将1到10之间的整数相加，如果累加值大于20，则跳出循环，并输出当前的累加值。

package work2;

public class work2 {

       public static void mian(String[] args){

              int sum=0;

              for(int i=0;i<=10;i++){

                     sum=sum+i;

                     if(sum>20){

                            System.out.println(sum);

                            break;

                     }

              }

       }

}     

---

（3）.求水仙花数(输出所有水仙花数)   水仙花数的定义：

/**

*运算规则:

*水仙花数是三位数，它的个、十、百位数字的立方的和等于该数本身，

*例如：371=27+343+1

package work3;

public class work3 {

       public static void main(String[] args){

              for(int x=100;x<=999;x++){

              int a,b,c;

              a=x/100;

              b=x/10%10;

              c=x%10;

              if(x==a*a*a+b*b*b+c*c*c){

                     System.out.println(x);

              }

              }

       }

}

---

（4）.输出菱形

       *

     ***

    *****

  *******

    ***** 

      ***  

        *

方法二：

package work4;

public class work4 {

       public static void main(String[] args){

              

              for(int j=1;j<5;j++){

                     for(int n=1;n<5-j;n++){

                            System.out.print(" ");

                     }

                     for(int i=2*j-1;i>0;i--){

                            System.out.print("*");

                     }

                     System.out.println("");

              }

              

              for(int j=3;j>0;j--){

                     for(int n=1;n<5-j;n++){

                            System.out.print(" ");

                     }

                            for(int m=2*j-1;m>0;m--){

                                   System.out.print("*");

                            }

                            System.out.println("");

                     }

              }

       }

运行结果：

---

空心菱形

方法一：

package work5;

public class work5 {

       public static void main(String[] args){

              for(int i=1;i<=4;i++){

                     for(int j=4-i;j>0;j--){

                            System.out.print(" ");

                     }

                            System.out.print("*");

                     if(i>1){

                     for(int m=1;m<=2*i-3;m++){

                            System.out.print(" ");

                     }

                            }

                     if(i>1){

                            System.out.print("*");

                            }

                     System.out.println("");

              }

              for(int i=3;i>0;i--){

                     for(int j=4-i;j>0;j--){

                            System.out.print(" ");

                     }

                            System.out.print("*");

                     if(i>1){

                     for(int m=1;m<=2*i-3;m++){

                            System.out.print(" ");

                     }

                            }

                     if(i>1){

                            System.out.print("*");

                            }

                     System.out.println("");

              }

       }

}

方法二：

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3.Scanner

Scanner sc = new Scanner(System.in);

              System.out.println("请输入行数：");

              int row = sc.nextInt();

              System.out.println(row);

sc.close();

---

4. 数组

什么是数组？

程序=算法+数据结构；

所谓数据结构，简单说就是把数据按照特定的某种结构来保存。

相同数据类型元素组成的集合。

数组下标越界异常提示：

java.lang.ArrayIndexOutOfBoundsException

数组的定义：

int[] arrInt2={1,2,3,4,5,6,7,8};

int[] arrInt3;

arrInt3=new int[]{1,2,3,4,5,6,7,8};

冒泡排序：

package work7;

import java.util.Arrays;

public class work7 {

      public static void main(String[] args) {

           // TODO Auto-generated method stub

           int[] arr={2,1,4,6,3};

           for(int i=1;i<arr.length;i++){

                 for(int j=0;j<arr.length-i;j++){

                      if(arr[j]>arr[j+1]){

                            int temp=arr[j];

                            arr[j]=arr[j+1];

                            arr[j+1]=temp;

                      }

                 }

           }

           System.out.println(Arrays.toString(arr));

      }

}