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1. ????

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1.1 ????

public static void main(String[] args) {    System.out.println(1);    System.out.println(2);    System.out.println(3);}

????????????????

2. ????

2.1 ?????? if

public static void main(String[] args) {    System.out.println("??");    int a = 10;    int b = 20;    if (a == b) {        System.out.println("a??b");    }    int c = 10;    if (a == c) {        System.out.println("a??c");    }    System.out.println("??");}

????????if???????????????????

2.2 if?else ??

public static void main(String[] args) {    int a = 1;    if (a % 2 == 0) {        System.out.println("a???");    } else {        System.out.println("a???");    }    System.out.println("??");}

??if?else??????????????????????????

2.3 if?else if ??

public static void main(String[] args) {    int x = 5;    int y;    if (x >= 3) {        y = 2 * x + 1;    } else if (x >= -1 && x < 3) {        y = 2 * x;    } else {        y = 2 * x - 1;    }    System.out.println("y????" + y);}

????????????????????????

3. ???? switch

switch?????????????????????????????byte?short?int?char?enum???JDK7????String???

public static void main(String[] args) {    int weekday = 6;    switch (weekday) {        case 1:            System.out.println("???");            break;        case 2:            System.out.println("???");            break;        case 3:            System.out.println("???");            break;        case 4:            System.out.println("???");            break;        case 5:            System.out.println("???");            break;        case 6:            System.out.println("???");            break;        case 7:            System.out.println("???");            break;        default:            System.out.println("????????");            break;    }}

?????case????break?????????????case???????

4. ????

????????????????????????

4.1 for??

// ??10?"HelloWorld"for (int x = 0; x < 10; x++) {    System.out.println("HelloWorld" + x);}

// ??1-100??????int sum = 0;for (int i = 1; i <= 100; i++) {    if (i % 2 == 0) {        sum += i;    }}System.out.println("sum?" + sum);

4.2 while??

public static void main(String[] args) {    int i = 1;    while (i <= 10) {        System.out.println("HelloWorld");        i++;    }}

while???????????????

4.3 do?while??

public static void main(String[] args) {    int x = 1;    do {        System.out.println("HelloWorld");        x++;    } while (x <= 10);}

do?while????????????????????????????????

5. ????

5.1 break??

????switch??????????????

public static void main(String[] args) {    for (int i = 1; i <= 10; i++) {        if (i == 3) {            break;        }        System.out.println("HelloWorld" + i);    }}

5.2 continue??

???????????????????

public static void main(String[] args) {    for (int i = 1; i <= 10; i++) {        if (i == 3) {            continue;        }        System.out.println("HelloWorld" + i);    }}