For-each loop in Java

Prerequisite: Decision making in Java
For-each is another array traversing technique like for loop, while loop, do-while loop introduced in Java5. 
 

• It starts with the keyword for like a normal for-loop.
• Instead of declaring and initializing a loop counter variable, you declare a variable that is the same type as the base type of the array, followed by a colon, which is then followed by the array name.
• In the loop body, you can use the loop variable you created rather than using an indexed array element. 
   
• It’s commonly used to iterate over an array or a Collections class (eg, ArrayList)

Syntax: 

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

Simple program with for each loop:

10 50 60 80 90 

The above syntax is equivalent to: 

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

The highest score is 132

Limitations of for-each loop 
       decision-making

1. For-each loops are not appropriate when you want to modify the array:
    

for (int num : marks) 
{
    // only changes num, not the array element
    num = num*2; 
}

       2. For-each loops do not keep track of index. So we can not obtain array index using For-Each loop 
 

for (int num : numbers) 
{ 
    if (num == target) 
    {
        return ???;   // do not know the index of num
    }
}

        3.  For-each only iterates forward over the array in single steps 
 

// cannot be converted to a for-each loop
for (int i=numbers.length-1; i>0; i--) 
{
      System.out.println(numbers[i]);
}

        4. For-each cannot process two decision making statements at once 
 

// cannot be easily converted to a for-each loop 
for (int i=0; i<numbers.length; i++) 
{
    if (numbers[i] == arr[i]) 
    { ...
    } 
}

        5. For-each also has some performance overhead over simple iteration: 

For each loop :: 45 ms
Using collection.size() :: 11 ms
By calculating collection.size() first :: 13 ms
Using [int j = list.size(); j > size ; j--] :: 15 ms

Related Articles: 
For-each in C++ vs Java 
Iterator vs For-each in Java