下面是一些关于如何迭代Set及其性能的技巧:

public class IterateSet {

    public static void main(String[] args) {

        //example Set
        Set<String> set = new HashSet<>();

        set.add("Jack");
        set.add("John");
        set.add("Joe");
        set.add("Josh");

        long startTime = System.nanoTime();
        long endTime = System.nanoTime();

        //using iterator
        System.out.println("Using Iterator");
        startTime = System.nanoTime();
        Iterator<String> setIterator = set.iterator();
        while(setIterator.hasNext()){
            System.out.println(setIterator.next());
        }
        endTime = System.nanoTime();
        long durationIterator = (endTime - startTime);


        //using lambda
        System.out.println("Using Lambda");
        startTime = System.nanoTime();
        set.forEach((s) -> System.out.println(s));
        endTime = System.nanoTime();
        long durationLambda = (endTime - startTime);


        //using Stream API
        System.out.println("Using Stream API");
        startTime = System.nanoTime();
        set.stream().forEach((s) -> System.out.println(s));
        endTime = System.nanoTime();
        long durationStreamAPI = (endTime - startTime);


        //using Split Iterator (not recommended)
        System.out.println("Using Split Iterator");
        startTime = System.nanoTime();
        Spliterator<String> splitIterator = set.spliterator();
        splitIterator.forEachRemaining((s) -> System.out.println(s));
        endTime = System.nanoTime();
        long durationSplitIterator = (endTime - startTime);


        //time calculations
        System.out.println("Iterator Duration:" + durationIterator);
        System.out.println("Lamda Duration:" + durationLambda);
        System.out.println("Stream API:" + durationStreamAPI);
        System.out.println("Split Iterator:"+ durationSplitIterator);
    }
}

代码是自解释的。

持续时间的结果是:

Iterator Duration: 495287
Lambda Duration: 50207470
Stream Api:       2427392
Split Iterator:    567294

我们可以看到Lambda耗时最长，而Iterator是最快的。

将集合转换为数组 也可以帮助你迭代元素:

Object[] array = set.toArray();

for(int i=0; i<array.length; i++)
   Object o = array[i];

然而，对于这个问题已经有了很好的答案。以下是我的回答:

1. set.stream().forEach(System.out::println); // It simply uses stream to display set values
2. set.forEach(System.out::println); // It uses Enhanced forEach to display set values

同样，如果这个集合是自定义类类型，例如:Customer。

Set<Customer> setCust = new HashSet<>();
    Customer c1 = new Customer(1, "Hena", 20);
    Customer c2 = new Customer(2, "Meena", 24);
    Customer c3 = new Customer(3, "Rahul", 30);

setCust.add(c1);
setCust.add(c2);
setCust.add(c3);
    setCust.forEach((k) -> System.out.println(k.getId()+" "+k.getName()+" "+k.getAge()));

//客户类:

class Customer{
private int id;
private String name;
private int age;

public Customer(int id,String name,int age){
this.id=id;
this.name=name;
this.age=age;
} // Getter, Setter methods are present.}

你可以使用一个增强的for循环:

Set<String> set = new HashSet<String>();

//populate set

for (String s : set) {
    System.out.println(s);
}

或者使用Java 8:

set.forEach(System.out::println);

下面是一些关于如何迭代Set及其性能的技巧:

public class IterateSet {

    public static void main(String[] args) {

        //example Set
        Set<String> set = new HashSet<>();

        set.add("Jack");
        set.add("John");
        set.add("Joe");
        set.add("Josh");

        long startTime = System.nanoTime();
        long endTime = System.nanoTime();

        //using iterator
        System.out.println("Using Iterator");
        startTime = System.nanoTime();
        Iterator<String> setIterator = set.iterator();
        while(setIterator.hasNext()){
            System.out.println(setIterator.next());
        }
        endTime = System.nanoTime();
        long durationIterator = (endTime - startTime);


        //using lambda
        System.out.println("Using Lambda");
        startTime = System.nanoTime();
        set.forEach((s) -> System.out.println(s));
        endTime = System.nanoTime();
        long durationLambda = (endTime - startTime);


        //using Stream API
        System.out.println("Using Stream API");
        startTime = System.nanoTime();
        set.stream().forEach((s) -> System.out.println(s));
        endTime = System.nanoTime();
        long durationStreamAPI = (endTime - startTime);


        //using Split Iterator (not recommended)
        System.out.println("Using Split Iterator");
        startTime = System.nanoTime();
        Spliterator<String> splitIterator = set.spliterator();
        splitIterator.forEachRemaining((s) -> System.out.println(s));
        endTime = System.nanoTime();
        long durationSplitIterator = (endTime - startTime);


        //time calculations
        System.out.println("Iterator Duration:" + durationIterator);
        System.out.println("Lamda Duration:" + durationLambda);
        System.out.println("Stream API:" + durationStreamAPI);
        System.out.println("Split Iterator:"+ durationSplitIterator);
    }
}

代码是自解释的。

持续时间的结果是:

Iterator Duration: 495287
Lambda Duration: 50207470
Stream Api:       2427392
Split Iterator:    567294

我们可以看到Lambda耗时最长，而Iterator是最快的。

至少有六种方法可以遍历一个集合。我了解到以下情况:

方法1

// Obsolete Collection
Enumeration e = new Vector(movies).elements();
while (e.hasMoreElements()) {
  System.out.println(e.nextElement());
}

方法2

for (String movie : movies) {
  System.out.println(movie);
}

方法3

String[] movieArray = movies.toArray(new String[movies.size()]);
for (int i = 0; i < movieArray.length; i++) {
  System.out.println(movieArray[i]);
}

方法4

// Supported in Java 8 and above
movies.stream().forEach((movie) -> {
  System.out.println(movie);
});

方法5

// Supported in Java 8 and above
movies.stream().forEach(movie -> System.out.println(movie));

方法6

// Supported in Java 8 and above
movies.stream().forEach(System.out::println);

这是我在例子中使用的HashSet:

Set<String> movies = new HashSet<>();
movies.add("Avatar");
movies.add("The Lord of the Rings");
movies.add("Titanic");