Java Foundation 2.5_ Program Logical Structure

Use the IF statement to determine

public class TestDemo {    public static void main(String args[]) {        double score = 90.0;        // 定义变量        if (score > 60.0) {     // 设置判断条件            System.out.println("及格了！");        }    }}程序执行结果： 及格了！

Use If...else to judge

public class TestDemo {    public static void main(String args[]) {        double score = 30.0;    // 定义变量        if (score > 60.0) {     // 条件判断满足            System.out.println("及格了！");        } else {            // 条件判断不满足            System.out.println("小白的成绩！");        }    }}程序执行结果： 小白的成绩！

Use If...else If...else to judge

public class TestDemo {    public static void main(String args[]) {        double score = 91.0;        // 定义变量        if (score < 60.0) {     // 条件判断            System.out.println("小白的成绩！") ;        } else if (score >= 60 && score <= 90) {// 条件判断            System.out.println("中等成绩") ;        } else if (score > 90 && score <= 100) {// 条件判断            System.out.println("优秀成绩") ;        } else {            // 条件判断都不满足            System.out.println("你家的考试成绩这么怪异！") ;        }    }}程序执行结果： 优秀成绩

Switch

For multi-conditional judgments, use IF. Else If...else can be judged by a Boolean condition, and if it is a majority, it can be done via switch with the following syntax

switch(整数 | 字符 | 枚举 | String) {    case 内容 : {        内容满足时执行 ;        break ;    }    case 内容 : {        内容满足时执行 ;        break ;    }    case 内容 : {        内容满足时执行 ;        break ;    } ...     default : {        内容都不满足时执行 ;        break ;    }}

  public class Testdemo {public static void main (String args[]) {int ch = 1;                Switch (CH) {//judge the number Case 2: {//Determine if the content is 2 System.out.println ("content is 2");            Break                } Case 1: {//Determine if the content is 1 System.out.println ("content is 1");            Break                } Case 3: {//Determine if the content is 3 System.out.println ("content is 3");            Break                } default: {//judgment does not satisfy System.out.println ("No matching content");            Break }}}} program execution result: content is 1  

public class TestDemo {    public static void main(String args[]) {        String str = "HELLO";        switch (str) {  // 判断的是字符串        case "HELLO": {            System.out.println("内容是HELLO");            break;        }        case "hello": {            System.out.println("内容是hello");            break;        }        case "mldn": {            System.out.println("内容是mldn");            break;        }        default: {            System.out.println("没有匹配内容");            break;        }        }    }}程序执行结果： 内容是HELLO

Achieve 1 to 100 accumulation--using the while loop

public class TestDemo {    public static void main(String args[]) {        int sum = 0;        // 保存总和        int current = 1;        // 循环的初始化条件        while (current <= 100) {    // 循环结束条件            sum += current;     // 累加            current++;  // 改变循环条件        }        System.out.println(sum);    }}程序执行结果： 5050

Use do. The while loop implements the additive operation

public class TestDemo {    public static void main(String args[]) {        int sum = 0;        // 保存总和        int current = 1; // 循环的初始化条件        do {    // 循环结束条件            sum += current; // 累加            current++;  // 改变循环条件        } while (current <= 100);   // 循环结束判断        System.out.println(sum);    }}程序执行结果： 5050

1 to 100 cumulative with for loop

public class TestDemo {    public static void main(String args[]) {        int sum = 0;        // 保存总和        // 设置循环初始化条件current，同时此变量作为累加操作使用        // 每次执行循环体前都要进行循环判断（current <= 100）        // 循环体执行完毕后会自动执行“current++”改变循环条件        for (int current = 1; current <= 100; current++) {            sum += current; // 循环体中实现累加操作        }        System.out.println(sum);    }}程序执行结果： 5050

Output multiplication Table

public class TestDemo {    public static void main(String args[]) {        for (int x = 1; x <= 9; x++) { // 控制循环的行数            for (int y = 1; y <= x; y++) {// 控制列数                System.out.print(x + "*" + y + "=" + (x * y) + "\t");            }            System.out.println();// 换行        }    }}1*1=1   2*1=2   2*2=4   3*1=3   3*2=6   3*3=9   4*1=4   4*2=8   4*3=12  4*4=16  5*1=5   5*2=10  5*3=15  5*4=20  5*5=25  6*1=6   6*2=12  6*3=18  6*4=24  6*5=30  6*6=36  7*1=7   7*2=14  7*3=21  7*4=28  7*5=35  7*6=42  7*7=49  8*1=8   8*2=16  8*3=24  8*4=32  8*5=40  8*6=48  8*7=56  8*8=64  9*1=9   9*2=18  9*3=27  9*4=36  9*5=45  9*6=54  9*7=63  9*8=72  9*9=81  

Loop control

Normally, as long as the loop is executed, the code of the loop body executes as long as the loop condition is met, but there are two loop-stop control statements in the program: Continue (exiting this loop), break (exiting the entire loop). Statements of this class tend to be judged in conjunction with branch statements when used.

Observe continue

public class TestDemo {    public static void main(String args[]) {        for (int x = 0; x < 10; x++) {            if (x == 3) {                continue; // 之后的代码不执行，直接结束本次循环            }            System.out.print("x = " + x + "、");        }    }}程序执行结果： x = 0、x = 1、x = 2、x = 4、x = 5、x = 6、x = 7、x = 8、x = 9、

Observe break

public class TestDemo {    public static void main(String args[]) {        for (int x = 0; x < 10; x++) {            if (x == 3) {                break; // 退出整个循环            }             System.out.print("x = " + x + "、");        }    }}程序执行结果： x = 0、x = 1、x = 2、

Java Foundation 2.5_ Program Logical Structure