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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);
}

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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);
}

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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);
    }
}

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??????if?switch?for?while???????????????????????????????????????????????????

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