if 选择结构
int a = 1;
if (a == 1) {
System.out.println("选项1");
} else if (a == 2) {
System.out.println("选项2");
} else {
System.out.println("无效选项");
}
if 嵌套结构
int a = 13;
if (a >= 0) {
if (a%2 == 1) {
System.out.println("a既是正数，也是奇数");
}
}
switch 选择结构
int a = 1;
switch (a) {
case 1 :
System.out.println("选项1");
break;
case 2 :
System.out.println("选项2");
break;
default :
System.out.println("无效选项");
}
for 循环结构
for (int a=1; a<10; a++) {
System.out.println(a);
}
while 循环结构
int a = 1;
while (a < 10) {
System.out.println(a++);
}
do…while 循环结构（至少循环一次）
int a = 10;
do {
System.out.println(a++);
} while (a < 10);
break 结束循环
for (int a=1; a<10; a++) {
if (a == 5) {
System.out.println("结束循环");
break;
}
System.out.println(a);
}
continue 跳过循环
for (int a=1; a<10; a++) {
if (a == 5) {
System.out.println("跳过循环");
continue;
}
System.out.println(a);
}
