冒号（:)运算符做什么？

Question

显然，Java中冒号以多种方式使用。有人介意解释它的作用吗？

例如这里：

String cardString = "";
for (PlayingCard c : this.list)  // <--
{
    cardString += c + "\n";
}

您将如何for-each以不同的方式编写此循环，以便不合并:？

Answer 1

在Java代码中冒号有几个地方：

1）跳出标签）：

label: for (int i = 0; i < x; i++) {
    for (int j = 0; j < i; j++) {
        if (something(i, j)) break label; // jumps out of the i loop
    }
} 
// i.e. jumps to here

2）三元条件：

int a = (b < 4)? 7: 8; // if b < 4, set a to 7, else set a to 8

3）每个循环：

String[] ss = {"hi", "there"}
for (String s: ss) {
    print(s); // output "hi" , and "there" on the next iteration
}

4）断言：

int a = factorial(b);
assert a >= 0: "factorial may not be less than 0"; // throws an AssertionError with the message if the condition evaluates to false

5）切换语句中的情况：

switch (type) {
    case WHITESPACE:
    case RETURN:
        break;
    case NUMBER:
        print("got number: " + value);
        break;
    default:
        print("syntax error");
}

6）方法参考

class Person {
   public static int compareByAge(Person a, Person b) {
       return a.birthday.compareTo(b.birthday);
   }}
}

Arrays.sort(persons, Person::compareByAge);