JAVA introductory system tutorial (5) Basic syntax (3)

Basic Grammar (3)

1. Loop statement: for / while / do...while

1) for loop

Format: for (loop variable initialization; loop variable condition; loop invariant change) {

                                                                                            using         use using ’s ’ using ’s ’ using ’ s ‐ ‐ ‐ ‐ ‐ ‐ ‐ ｝ ｝

                 1>Execute the loop variable initialization part and set the loop initialization status. This part is only executed once in the loop

Judge the loop condition. If it is true, the code in the loop will be executed. If it is false, exit the loop directly

                                                                                                                                                                     

(Note: There is no need to add semicolons where there are braces, and there is no need to add braces where there are semicolons)

Example question : Sum, find the sum of 1~100

##2) while loop

Format: while (judgment condition){

                                                                                                          ’ s ’ s ‐       ‐ ‐ ‐ ‐ ‐ to # Execution process:

Determine whether the condition behind while is true

Example: Enter 1-5

in succession 3) do...while loop

Format: do｛

｝ While (Judgment Conditions)

：:

& LT; 1 & GT;

# If it is true, continue to execute until it is not true and end the loop

Example: Calculate the sum of even numbers within 50

## 4) Loop Nesting

Example: Type a 9X9 multiplication table

ps: continue: Stop the current loop and enter the next step A loop, break: end the loop

2. Array: An array can be understood as a huge box, which can store multiple data of the same type in order.

As shown below

The elements can be accessed through subscripts

The subscripts of the array start from 0, that is, score[0 here ] = 76 . . . . . . score[3] = 87

Initialization of the array: 1) Dynamic initialization: Specify the length of the array, and the system will assign values ​​to the elements in the array

(The format here is: data type [ ] array name = new array type [specified length] )

2) Static initialization: Specify the value of the element in the array, and the system will specify the length of the array

              Treatment of data in the array: We can operate and process the array of the assigned value

# We can directly create an array method. Merging completed

                                                                                                                                                                                                to be completed, such as: int[ ] sc = new int[ ]{5,15,25,35,48,55,38}

                       Array: length attribute: Get the length of the array

Example: Enter a set of data and output the array

3. Method: Method It is an ordered combination of codes used to solve a type of problem, that is, a functional module

Syntax: access modifier return value type method name (parameter list) {

Method Sports

# 1) Access decoration: Method allows the scope of permissions to be accessed. , the use of other modifiers will be explained in detail in later chapters

2) Return value type: the type of the method return value, if the method does not return any value, the return value type is specified as void; if If the method has a return value, you need to specify the type of the return value, and use the return statement in the method body to return the value

3) Method name: The name of the defined method must use a legal identifier

4) Parameter list: Parameter list passed to the method. There can be multiple parameters. Multiple parameters are separated by commas. Each parameter consists of parameter type and parameter name, separated by spaces

Methods can be divided into four categories according to whether they have parameters and return values:

Ø Methods without parameters and return values

Ø Methods without parameters and return values

Ø Method with parameters and no return value

Ø Method with parameters and return value

Calling method:
1) Single call: no specific result
2) Output call: not enough Okay, the data is hard-coded and output directly. There is no further requirement for the results
3) Assignment call

Example: In the previous example, we added a method to optimize the sorting process.

Question: Based on what we have learned before, we will make a set of more complex program requirements as follows

1) Input a set of arrays 2) Output the array 3) Inverse output of the array 4) You can filter out the maximum and minimum numbers and output them 5) Add data query function 6) Use methods to optimize the program process

package example;


import java.util.Scanner;


public class Ex1 {  public static void main(String[] args) {        @SuppressWarnings("resource")           Scanner sc = new Scanner(System.in);            int[] score = new int[5];           for(int i = 0 ; i<=score.length-1 ; i++) {               System.out.println("请输入第"+(i+1)+"个数");              int x = sc.nextInt();
                    score[i] = x;           }           System.out.print("您输入的数组为：");
                printArray(score);
                max(score, 0);
                min(score, 0);
                nx(score,0);
                printArray(score);
                where(score);   }       //遍历数组方法    public static void printArray(int[] score) {        for(int x = 0 ; x<=score.length-1 ; x++) {           if(x==0) {              System.out.print("[ "+score[x]);            }else if(x==score.length-1) {               System.out.print(" "+score[x]+" ]");            }else {             System.out.print(" "+score[x]);         }       }       System.out.println("");     System.out.println("------------------------"); }       //输出最大值方法   public static void max(int[] score, int max) {      max = score[0];     for(int y = 1 ; y<=score.length-1 ; y++) {           if (max<score[y]) {              max = score[y];         }       }   System.out.println("您输入的最大值为："+max);    System.out.println("------------------------"); }       //输出最小值方法   public static void min(int[] score, int min) {      min = score[0];     for(int y = 1 ; y<=score.length-1 ; y++) {           if (min>score[y]) {              min = score[y];         }       }   System.out.println("您输入的最小值为："+min);    System.out.println("------------------------"); }       //逆序方法  public static void nx(int[] score,int temp) {       for(int y = 0 ; y<=(score.length-1)/2 ; y++) {           temp = score[y];            score[y]=score[score.length-1-y];           score[score.length-1-y]=temp;       }       System.out.print("该数组的逆序为：");   }       //查找数据方法    public static void where(int[] score) {     @SuppressWarnings("resource")       Scanner sc = new Scanner(System.in);        System.out.print("请输入您要查找的数：    ");     int ex = sc.nextInt();      for(int y = 0 ; y<score.length ; y++) {          if(ex == score[y]) {                System.out.println("您输入的是第 "+(y+1)+" 个数");              break;          }else if(ex!=score[0] && ex!=score[1] && ex!=score[2] && ex!=score[3] && ex!=score[4]) {                System.out.println("没有您要找的数");              break;          }       }   }                   }

Supplement: Method overloading

If the same class contains two or more methods with the same method name and different number, order or type of method parameters, It is called the overloading of the method, and it can also be said that the method is overloaded. As shown below, the four method names are all show, but the parameters of the methods are different, so they are all overloaded methods:

##How to distinguish which overloaded method is called?

When calling an overloaded method, Java will determine which overloaded method should be called based on the number and type of parameters. The method with completely matching parameters will be executed

The result at this time is:

PS: Basis for judging method overloading

1. Must be in the same class
2. Method The names are the same
3. The number, order or type of method parameters are different

4. It has nothing to do with the modifiers or return values ​​of the methods

#END

#Related articles:

JAVA Getting Started System Tutorial (3) Basic Grammar (1)

JAVA introductory system tutorial (4) Basic syntax (2) ######

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