java - 'for' 循环可替换为 'foreach'

Question

我的代码是:

ArrayList<People> people = new ArrayList<>();

// people.add(...);
// people.add(...);

        for (int i = 0; i < people.size(); i++) {
            if (people.get(i) > 60.0)
                System.out.println(people.get(i).toString());
        }

我收到以下警告:

'for' loop replaceable with 'foreach'

我应该如何使用 foreach 修改循环？

谢谢。

Answer 1

名为people 的列表通常包含Person 对象。

下面是一些示例代码，展示了如何使用 for-each 循环:

public class Demo {

    private static class Person {
       public int age;
       public String name;

       public Person(int age, String name) {
           this.age = age;
           this.name = name;
       }
    }

    public static void main(String... args) {

        // Create and populate a list of people with individuals
        List<Person> people = new ArrayList<>();
        people.add(new Person(32, "Fred"));
        people.add(new Person(45, "Ginger"));
        people.add(new Person(66, "Elsa"));

        // Iterate over the list (one person at a time)
        for (Person person : people) {
            if (person.age > 60) {
                System.out.println("Old person: " + person.name);
            }
        }
    }
}

您还可以阅读 Oracle Java documentation about for-each loops .

一般形式是:

for (Person person : people) {
    ...
}

代替:

for (int i = 0; i < people.size(); i++) { 
    Person person = people.get(i);
    ...
}

通常推荐使用 for-each，因为它更简洁。 但是，如果您需要知道您必须使用的项目的索引号 原始的 for 循环或在 for-each 中增加一个计数器。