##Process control

JAVA input and output

Input

Two input methods:

Method 1: java.util.Scanner

The code is as follows:

public class a {
    public static void main(String[] args) {
        var sc = new Scanner(System.in);
        System.out.println("請輸入姓名：");
        String name = sc.nextLine();
        System.out.printf("%n歡迎你：%s", name);
    }}

Generate a Scanner object, output "Please enter your name:", return the input string and assign it to name, and output "%nWelcome %s" where %n represents a newline and %s represents name

Result:

Method 2: JOptionPane If the input content is confirmed, the string value will be null

public class a {
    public static void main(String[] args) {
        String w = JOptionPane.showInputDialog("請輸入詞匯：");
        System.out.println(w);
    }}

Result:

Output

Three ways to output on the console

Method 1: System.out.print (); Output to the console
Method 2: System.out.println(); Output to the console and wrap
Method 3: System.out.printf(); Format the output to the console

Code demonstration:

The first method outputs directly without line breaks

public class a {
    public static void main(String[] args) {
        int w = 1;
        int a = 2;
        System.out.print(w);
        System.out.print(a);
    }}

Result:

The second line feed output

public class a {
    public static void main(String[] args) {
        int w = 1;
        int a = 2;
        System.out.println(w);
        System.out.println(a);
    }}

Result:

The third formatted output

The meaning of %d It is an int type variable, that is, replace the first %d with the value of w, and replace the second %d with the value of a

public class a {
    public static void main(String[] args) {
        int w = 1;
        int a = 2;
        System.out.printf("w=%d a=%d", w, a);
    }}

Result:

Branch statement

if else

if() The condition in the brackets returns true as long as it is correct, and false if it is wrong.

else means otherwise

public class a {
    public static void main(String[] args) {
       if (1>2){
           System.out.println("A");
       }else {
           System.out.println("B");
       }
    }}

Multiple judgments are as follows: If the first judgment is incorrect, the next judgment will be made. When the return value is true, it will be executed, otherwise else## will be executed.

#

public class a {
    public static void main(String[] args) {
        if (1 > 2) {
            System.out.println("A");
        } else if (1 > 0) {
            System.out.println("B");
        } else {
            System.out.println("C");
        }
    }}

switch case default

#switch multi-branch switch statement

switch(w) w in brackets is the judgment parameter, and the number after case is A value that matches w. When the value of w matches the value after the case, the statement in the current case is executed

break means to exit the current judgment, which means that there is no need to judge again later
default means the default value, when there is no match The default is this

public class a {
    public static void main(String[] args) {
        int w=1;
        String wk = "";
        switch (w) {
            case 2:
                wk = "星期一";
                break;
            case 3:
                wk = "星期二";
                break;
            case 4:
                wk = "星期三";
                break;
            case 5:
                wk = "星期四";
                break;
            case 6:
                wk = "星期五";
                break;
            case 7:
                wk = "星期六";
                break;
            default:
                wk = "星期日";
                break;
        }
        System.out.println(wk);
    }}

result:

Loop statement

for

for ( int i = 0; i < 5; i ) is divided into three parts. int i=0 is the initial value, i<5 is the loop condition, and i is the value of i plus 1 after executing this statement once. Exit the loop when i>5

public class a {
    public static void main(String[] args) {
        for (int i = 0; i < 5; i++) {
            System.out.println(i);
        }
    }}

Result:

for in

for in is mainly used to loop collections Or an array, use an array to demonstrate

public class a {
    public static void main(String[] args) {
        int[] a = {1, 2, 3, 4, 5};
        for (int i : a) {
            System.out.println(i);
        }
    }}

i corresponds to the value in the table below of array a, which is equivalent to looping output a[0],a[1]a[2],a [3]The value of a[4]

while do while

while(condition){ }
• Execute the statement if the condition is met, exit if not.

  
  

public class a {
    public static void main(String[] args) {
        int i = 0;
        while (i < 5) {
            i++;
            System.out.println(i);

        }
    }}

Result:

do while

Different from while, do while is executed once Then judge

public class a {
    public static void main(String[] args) {
        int i = 0;
        do {
            i++;
            System.out.println(i);

        } while (i < 0);
    }}

The output is executed first and then judged. Therefore, the condition i<0 can also output once

The result is:

break continue

break;

Terminate the current loop statement continue;
End this loop and immediately prepare to start the next loop

int i = 0;while (++i < 20) {
    if (i % 2 == 0) continue;
    System.out.println(i);
    if (i > 10) break;}

Skip this time when i is divisible by 2 , proceed to the next cycle. When i is greater than 10, the loop ends.

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