Chapter 1 of JAVASE, Chapter 3, program control and array, and javase

Chapter 1 of JAVASE, Chapter 3, program control and array, and javase
Purpose:
1. You can understand the three structures of the program.
2. You can understand one-dimensional arrays, two-dimensional arrays, multi-dimensional arrays, and irregular arrays.
3. You can understand Shift Operators and random numbers.


Three structures of 1 program
Code execution from top to bottom in a sequential structure
Select the statement to determine the execution sequence of the code based on the logic
Loop statements repeatedly execute a code block based on logic


2 SELECT statement
1) if statement
1/Direct output
2/if... else
3/if... else if...
4/if, for example, (a> B )? A/B: a * B


2) switch statement
Switch statement: Only byte, int, char, and short enumeration types are allowed.
Statement format: switch (variable)
{
Case variable 1: Statement Block 1; break;
Case variable 2: Statement Block 2; break;
Default: statement;
}


3. Loop statements
1) while statement
Statement features: Judge first and then execute a loop


2) do... while statement
Statement features: execute a loop at least once before determining


3) for Loop


4 keywords
Break: jump out of the loop body and close the loop directly.
Continue: abort this loop, directly next loop.


5 arrays
1) array declaration and initialization
A Dynamic Expression int [] array name = new int [number of arrays]
B static initialization int [] array name = new int [] {array value 1, array value 1 ...}
Int [] array name = {array value 1, array value 1 ...}
2) array subscript (also called array index)
The subscript of array a starts from 0.
B. Do not access non-existing array elements, which exceed the orientation of array elements.


3) Length of the array
A uses array name. length to get the array length.
B code, length Traversal


4) default and initialization of Arrays
A defines an array but does not assign values to the array. In this case, the system will initialize the array by default.
B Note: The default value of byte short int float dobuble is 0, and the default value of Boolean is flase.


5) Conversion
A converts a string to a character.
String str = "strValue ";
Char charVal = str. charAt (0 );


B. Convert the string to a struct array.
String str = "strValue ";
Char [] charArray = str. toCharArray ();


6) two-dimensional array
A display Initialization
1/int [] [] results = {1, 2, 3}, {1, 2, 3}; // {initial value of the first row}, {initial value of the second row }, {initial value of the third row }...}
2/int [] [] results = new int [] [] {1, 2, 3}, {1, 2, 3 }};


B Application
1/matrix conversion => convert rows and column elements of a two-dimensional array and store them in another two-dimensional array.
2/Yang Hui triangle => its oblique edge is composed of numbers 1, while the remaining number is the sum of the two numbers on his shoulder.


C understanding
1/array: Used as a linear graph in ry.
2/two-dimensional array: equivalent to a table


7) multi-dimensional array
The dimension of the array is the logarithm of brackets after the type.
Number of multi-dimensional array elements = the product of the size on each two-dimensional


8) Irregular array and rule Array
Rule array: linear distribution, with the same number of elements per line
Irregular array: the number of elements in each row is different.
A irregular array definition: Because multidimensional arrays are not linearly allocated in memory, they can exist in irregular forms.
B, such as 1/int [] [] results = {1, 2, 3}, {5, 7}, {0 }}
2/int [] [] x = new int [5] []
Row 0 has four elements => x [0] = new int [4] 1 has three elements => x [1] = new int [3]...


6 Shift Operators
> Shifts to the right once, which is equal to dividing by 2 (moving two places to the right and adding 1 to the right)
<Shifts to the left once, which is equivalent to multiplying 2 (shifts two places to the left, and adds 0 to the left)
>>> Shifts two places to the right, and adds 0 to the left (no <operator)


7 small applications
A generates a random number.
Int num = new java. util. Random (). nextInt (10); // Random Number 1-10


B input from the keyboard. An input box is displayed.
String obj_str = javax. swing. JOptionPane. showInputDialog ("input number :");
Int num_int = Integer. parseInt (obj_str );
Double num_dou = Double. parseDouble (obj_str );