[Java process control learning] loop structure

Cyclic structure

while loop

//输出1-100

int i=0;
while(i<100){
    
    
    i++;
    System.out.println(i);
}

//计算1+2+3...100=?
int i=0;
int sum=0;
while(i<100){
    
    
    i++;
    sum=sum+i;
}
System.out.println(sum);

Pseudo code (endless loop)

Such as server request response monitoring, etc.

while(true){
    
    
    //等待客户端连接,定时检查
}

do...while loop

The difference with while: execute at least once, and then loop; while while may not loop once

//计算1+2+3...100=?
int i=0;
int sum =0;
do {
    
    
    sum=sum+i;
    i++;
}while (i<=100);
System.out.println(sum);

for loop

Syntax format:

for(initialization; Boolean expression; update) {

//Code statement

}

Can be empty (endless loop):

for（ ；；）{}

int sum=0;
for(int i=0;i<=100;i++){
    
    
    sum=sum+i;  //i++在语句执行之后再执行
}
System.out.println(sum);

IDEA shortcut key: 100.for

//1：计算 0到100 之间奇数和偶数的和
int oddSum =0;
int evenSum =0;
for (int i = 0; i <= 100; i++) {
    
    
    if (i%2!=0){
    
    
        oddSum+=i;
    }else{
    
    
        evenSum+=i;
    }
}
System.out.println("奇数的和："+oddSum);
System.out.println("偶数的和："+evenSum);

//2：用for循环输出1-1000之间能被5整除的数，并且每行输出3个

int j=0;
for (int i = 1; i <= 1000; i++) {
    
    
    if (i%5==0){
    
    
        System.out.print(i+"\t");
        j++;
        if (j%3==0){
    
    
            System.out.print("\n");
           //等同于System.out.println("");
        }
    }

}

The difference between print and println

• print: do not wrap after output

• println: Automatically wrap after output

• System.out.print("\n");等同于System.out.println("");

  Tab character (space): "\t"

  Newline character: "\n"

  //3.打印九九乘法表
  for (int i = 1; i <=9; i++) {
        
        
      for (int j = 1;  j<= i; ++j) {
        
        
  
          System.out.print(j + "*" + i + "=" + j * i + "\t");
  
      }
      System.out.println();
  }
  /*
  输出:
  1*1=1	
  1*2=2	2*2=4	
  1*3=3	2*3=6	3*3=9	
  1*4=4	2*4=8	3*4=12	4*4=16	
  1*5=5	2*5=10	3*5=15	4*5=20	5*5=25	
  1*6=6	2*6=12	3*6=18	4*6=24	5*6=30	6*6=36	
  1*7=7	2*7=14	3*7=21	4*7=28	5*7=35	6*7=42	7*7=49	
  1*8=8	2*8=16	3*8=24	4*8=32	5*8=40	6*8=48	7*8=56	8*8=64	
  1*9=9	2*9=18	3*9=27	4*9=36	5*9=45	6*9=54	7*9=63	8*9=72	9*9=81	
  */
  

Enhanced for loop

: Introduced by java5, used to loop arrays and collection objects

int[] numbers = {
    
    10,20,30,40,50};  //定义一个数组

for (int i = 0; i < 5; i++) {
    
    
    System.out.println(numbers[i]);
}
System.out.println("======================================");

//遍历数组的元素
for (int x:numbers){
    
    
    System.out.println(x);
}


/*
输出结果：
10
20
30
40
50
======================================
10
20
30
40
50
*/