Many Xiaobai feel that printing patterns burns their brains after learning the cycle , In fact, this kind of topic is mainly to make you more understand the use of recycling , Don't worry because you can't think of it , Just step by step , Let's start with simple to difficult topics

5*5 Square

We want to print 5*5 The square of , According to what we have learned before, we can understand this first

// Use single layer cyclic printing 
for(int i = 1;i<=5;i++){
    
	System.out.print("*****"+"\t");
}

It can be seen that the effect can be printed with single-layer cycle , So we think what if the pattern to be printed is not the same for each column , At this time, we think of adding another layer of circulation

for(int i = 1;i<=5;i++){
    
	for(int j = 1;j<=5;j++){
    
	System.out.print("*"+"\t");
	}
}

A comparison of the first two found , The first layer of loop can control rows , The second control column
Running results :

99 Multiplication table

Go straight to the code

public class MultiplicationTables99{
    
	public static void main(String[] args){
    
		for(int i=1;i<=9;i++){
    // That's ok 
			for(int j=1;j<=i;j++){
    // Column 
				System.out.print(j+"*"+i+"="+i*j+"\t");// Format of multiplication table 
			}
			System.out.println();// Output line feed 
		}
	}
}

Running results ：

Use a single-layer cycle to do

public class MultiplicationTables99{
    
	public static void main(String[] args){
    
		int j = 1;
		for(int i=1;i<=9;i++){
    // That's ok 
			System.out.print(j+"*"+i+"="+i*(j++)+"\t");// Format of multiplication table 
			if(j>i){
    // It's equivalent to replacing the second layer of loop 
				j = 1;
				i++;
				System.out.println();
			}
		}
	}
}

just （ pour ） Triangle

public class ZhengTriangle{
    
	public static void main(String[] args){
    
		for(int i=1;i<=5;i++){
    // The control line 
			for(int k=5;k>i;k--){
    // Print space 
				System.out.print(" ");
			}
			for(int j=1;j<=i;j++){
    // Print "*"
				System.out.print("*"+" ");
			}
				System.out.println();
		}
	}
}

Running results ：

Inverted triangle

public class DaoTriangle{
    
	public static void main(String[] args){
    
		for(int i=1;i<=5;i++){
    // Print row 
			for(int k=1;k<i;k++){
    // Can be replaced by "k--"
				System.out.print(" ");// Print space 
			}
			for(int j=5;j>=i;j--){
    
				System.out.print("*"+" ");// Print "*"
			}
				System.out.println();
		}
	}
}

Running results ：

Yang hui triangle

The printing of Yang Hui triangle requires a two-dimensional array , First, we observe the law , It can be found that we can first determine the number of rows and columns , So define a two-dimensional array , And when i=j perhaps j=0 The time is 0, And the laws of other ranks meet arrys[i][j] = arrys[i-1][j]+arrys[i-1][j-1]; Then let it be

public class YangHui{
    
	public static void main (String[] args){
    
		// Create a row and column as 10 Two dimensional array of 
		int arrys[][] = new int [10][10];
		// first floor for Loop controls the number of rows , The second layer controls the number of columns 
		for(int i = 0;i<arrys.length;i++){
    
			for(int j = 0;j<i+1;j++){
    
				// Observation shows that if i=j Hour or second 0 Column time , by 1
				if(i==j || j == 0){
    
					arrys[i][j] = 1;
				}else {
    
					// The other ranks follow the rules , Let this be the number one i That's ok , The first j Column , be 
					// It will be equal to (i-1,j),(i-1,j-1) The sum of the values corresponding to the subscript 
					arrys[i][j] = arrys[i-1][j]+arrys[i-1][j-1];
				}
				 System.out.print(arr[i][j]+"\t");
			}
				System.out.println();
		}
	}
}

Running results ：