Java：冒号（:)运算符是做什么的？ [英] Java: What does the colon (:) operator do?

问题描述

我会自己去看，但是我甚至不知道它叫什么。有人会介意解释它做什么？

我不知道有多少次出现。在这种情况下，它在这里做了什么：

  public String toString（）{
 String cardString =; （PlayingCard c：this.list）的
 //<  -  
 {
 cardString = cardString + c +\\\
; 
 
 $ / code $ / pre 
 
 
你怎么写这个 code>循环不同的方式，以便不纳入：？
解决方案
有几个地方冒号是在Java代码中使用： 
 
 <1>跳出标签（ 
 $ p $  label：for（int i = 0; （int（i，j））{
 if（something（i，j））break label; //跳出i循环
} 
} 
 // ie跳转到这里
  

2）三元条件（教程 ）：



  int a =（b <4）？ 7：8; //如果b < 4，设a为7，否则设a为8 
  



3）对于每个循环（教程）：



  String [] ss = {hi，there} 
 for（String s：ss）{
 print（s）; //在下一次迭代中输出hi和there
} 
  

4 ）声明（指南）：

  int a = factorial（b）; 
声明一个> = 0：阶乘不得小于0;如果条件计算结果为false，则抛出一个AssertionError消息
  

5）switch语句中的case 教程）：



  switch（type）{
 case WHITESPACE：
 case返回：
 break; 
 case NUMBER：
 print（got number：+ value）; 
 break; 
默认值：
 print（syntax error）; 
 
 
 
 
 
 6）方法引用（
  class Person {
 public static int compareByAge（Person a，Person b）{
 return a.birthday.compareTo（b.birthday）; 
}} 
} 
 
 Arrays.sort（persons，Person :: compareByAge）; 
  
 
I would look it up myself, but I don't even know what it's called. Would anyone mind explaining what it does? 

I didn't know there were multiple times the : appeared. What does it do in this case here:
public String toString() {
    String cardString = "";
    for (PlayingCard c : this.list)  // <--
    {
        cardString = cardString + c + "\n";
    }
How would you write this for-each loop a different way so as to not incorporate the ":"?
解决方案
There are several places colon is used in Java code:

1) Jump-out label (Tutorial):
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) Ternary condition (Tutorial):
int a = (b < 4)? 7: 8; // if b < 4, set a to 7, else set a to 8
3) For-each loop (Tutorial):
String[] ss = {"hi", "there"}
for (String s: ss) {
    print(s); // output "hi" , and "there" on the next iteration
}
4) Assertion (Guide):
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) Case in switch statement (Tutorial):
switch (type) {
    case WHITESPACE:
    case RETURN:
        break;
    case NUMBER:
        print("got number: " + value);
        break;
    default:
        print("syntax error");
}
6) Method references (Tutorial)
class Person {
   public static int compareByAge(Person a, Person b) {
       return a.birthday.compareTo(b.birthday);
   }}
}

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


                        
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