Java ArrayDeque forEach()方法

ArrayDeque的 forEach() 方法是继承自java.lang.Iterable接口。如果该方法指定了迭代的顺序，那么该操作将按照迭代的顺序进行。方法遍历ArrayDeque的Iterable中的每个元素，直到所有的元素都被方法处理完或者发生异常。由操作抛出的异常会传递给调用者。

语法

public void forEach(Consumer<? super E> action)

参数： 该方法接受一个参数名称 action ，表示对每个元素要进行的操作。

返回： 该方法返回Nothing。

异常： 如果指定的动作为空，该方法会抛出NullPointerException。

下面的程序说明了ArrayDeque的forEach()方法。

例1： 演示ArrayDeque的forEach()方法，ArrayDeque包含一个字符串值的队列。

// Java Program Demonstrate forEach()
// method of ArrayDeque
  
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // create an ArrayDeque
        // which contains string values
        ArrayDeque<String> cities = new ArrayDeque<String>();
  
        // Add Strings to list
        cities.add("Kolkata");
        cities.add("Delhi");
        cities.add("Bombay");
        cities.add("Pune");
  
        // forEach method of ArrayDeque and
        // print city names
        cities.forEach((n) -> System.out.println(n));
    }
}

输出。

Kolkata
Delhi
Bombay
Pune

例2： 演示ArrayDeque上的forEach()方法，ArrayDeque包含对象队列。

// Java Program Demonstrate forEach()
// method of ArrayDeque
  
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // create an ArrayDeque which going to
        // contains a list of Objects
        ArrayDeque<batch> list = new ArrayDeque<batch>();
  
        // Add Objects to list
        list.add(new batch("CSE", 67));
        list.add(new batch("ECE", 57));
        list.add(new batch("IT", 90));
        list.add(new batch("ME", 78));
  
        // print result
        System.out.println("list of Objects:");
  
        // forEach method of ArrayDeque and
        // print student names
        list.forEach((n) -> print(n));
    }
  
    // printing details of object
    public static void print(batch n)
    {
        System.out.println("*******************************");
        System.out.println("Batch Name is " + n.name);
        System.out.println("No of Students are " + n.noOfStudents);
    }
}
  
// create a class
class batch {
  
    String name;
    int noOfStudents;
  
    batch(String name, int noOfStudents)
    {
        this.name = name;
        this.noOfStudents = noOfStudents;
    }
}

输出。

list of Objects:
*******************************
Batch Name is CSE
No of Students are 67
*******************************
Batch Name is ECE
No of Students are 57
*******************************
Batch Name is IT
No of Students are 90
*******************************
Batch Name is ME
No of Students are 78

例3： 演示ArrayDeque上forEach()方法的NullPointerException。

// Java Program Demonstrate forEach()
// method of ArrayDeque
  
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // create an ArrayDeque
        // which contains string values
        ArrayDeque<String> cities = new ArrayDeque<String>();
  
        // Add Strings to list
        cities.add("Kolkata");
        cities.add("Delhi");
        cities.add("Bombay");
        cities.add("Pune");
  
        try {
            // forEach method of ArrayDeque and
            // print city names
            cities.forEach(null);
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

输出。

Exception: java.lang.NullPointerException

参考资料：
https://docs.oracle.com/javase/10/docs/api/java/util/ArrayDeque.html#forEach(java.util.function.Consumer)。