JAVA process control method

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("请输入姓名：");
        String name = sc.nextLine();
        System.out.printf("%n欢迎你：%s", name);
    }}

Generate a Scanner object, output "Please enter your name:", return the input string and assign a value For name, output "%nWelcome %s" where %n means line break %s means name

Result:

Method 2: JOptionPane input content If it is determined, it will be a string value. As long as it is not determined, it will be null

public class a {
    public static void main(String[] args) {
        String w = JOptionPane.showInputDialog("请输入词汇：");
        System.out.println(w);
    }}

Result:

Output

Three ways to output on the console
Method one: System.out.print(); Output to the console
Method two: System.out.println(); Output to the console and wrap
Method three: System.out.printf(); format output to the console

Code demonstration:

The first method does not have newlines Direct output

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

Result:

Second line break 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
%d means an int type variable, that is, replacing the first %d with the value of w, and replacing 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() As long as the conditions in brackets are correct It returns true, if it is wrong, it returns false
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 not correct, proceed to the next judgment. When the return value is It is executed when true, otherwise it is executed else

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, after case The number is the 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

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

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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