For-each循环

For-each循环一般用于遍历数组或集合类（例如，ArrayList）。

句法：

for (type var : array) 
{ 
    statements using var;
}

相当于：

for (int i=0; i<arr.length; i++) 
{ 
    type var = arr[i];
    statements using var;
}

For-each循环的实例：

// Java program to illustrate
// for-each loop
class For_Each    
{
    public static void main(String[] arg)
    {
        {
            int[] marks = { 125, 132, 95, 116, 110 };
              
            int highest_marks = maximum(marks);
            System.out.println("The highest score is " + highest_marks);
        }
    }
    public static int maximum(int[] numbers)
    {
        int maxSoFar = numbers[0];
          
        // for each loop
        for (int num : numbers)
        {
            if (num > maxSoFar)
            {
                maxSoFar = num;
            }
        }
    return maxSoFar;
    }
}

输出：

The highest score is 132

但是for-each也有其局限性，更多可以参照：在Java中的For-each循环

循环的陷阱

无限循环：实现任何类型的循环时最常见的错误之一是，它可能永远不会退出，也就是循环运行无限的时间。出于某种原因，条件失败时会发生这种情况。
例子：

//Java program to illustrate various pitfalls.
public class LooppitfallsDemo
{
    public static void main(String[] args)
    {
 
        // infinite loop because condition is not apt
        // condition should have been i>0.
        for (int i = 5; i != 0; i -= 2)
        {
            System.out.println(i);
        }
        int x = 5;
 
        // infinite loop because update statement
        // is not provided.
        while (x == 5)
        {
            System.out.println("In the loop");
        }
    }
}

另一个缺陷是你可能通过循环向你的collection对象中添加了一些东西，你可能会用完内存。如果尝试执行下面的程序，一段时间后，内存不足异常将被抛出。

//Java program for out of memory exception.
import java.util.ArrayList;
public class Integer1
{
    public static void main(String[] args)
    {
        ArrayList<Integer> ar = new ArrayList<>();
        for (int i = 0; i < Integer.MAX_VALUE; i++)
        {
            ar.add(i);
        }
    }
}

输出：

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Unknown Source)
at java.util.Arrays.copyOf(Unknown Source)
at java.util.ArrayList.grow(Unknown Source)
at java.util.ArrayList.ensureCapacityInternal(Unknown Source)
at java.util.ArrayList.add(Unknown Source)
at article.Integer1.main(Integer1.java:9)