For - Java

Definition §

A for loop runs for a specified number of cycles, either denoted by a variable or implicitly by the size of the array.

for (_dataType_ _counter_ = _value_; _counter_ <= _guardian_; _counter__increment_){
	statement executed each time;
}

For loops headers are comprised of three main parts:

• The starting bound _value_
• The ending bound _guardian_
• The value by which we want to increase the _counter_, _increment_

This can be read as: “For each _dataType_ _counter_ incremented by _increment_, do something.” Consider the following loop:

for (int i = 0; i < ourMaxValue; i++){
	System.out.println(i);
}

This can be read as: “For each int i incremented by 1, print i.”

See: [[#Applications#For Loop]]

Enhanced For Loop §

Also referred to as a For-Each loop, an enhanced for loop is designed for use with arrays.

for (_arrayDataType_ _variable_ : _arrayName_){
	statement;
}

For loops can be read as: “For each _arrayDataType_ _variable_ of _arrayName_, do something.” Consider the following loop:

for (Person p : personsArray) {
	System.out.println(p.getName());
}

This can be read as: “For each Person p of the personsArray array, print p.getName().”

See: [[#Applications#Enhanced For Loop]]

Applications §

For Loop §

int[] ints = { 1, 2, 3, 4 };
 
int sumOfInts = 0;
 
for (int i = 0; i < ints.length; i++) {
	sumOfInts += ints[i];
}
 
System.out.println(sumOfInts);
 
/* Output:
	10
*/

Enhanced For Loop §

// Define your array
ArrayList<Integer> intArray = new ArrayList<>();
 
ints.add(1);
ints.add(2);
ints.add(3);
 
for (Integer i : intArray){
	System.out.println(intArray.get(i - 1)); 
}
 
/* Output:
	1
	2
	3
*/

Note that in the above code, we subtract 1 from i to prevent out of bounds errors. Had we left it as intArray.get(i), we would receive the following output:

2
3
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index 3 out of bounds for length 3
        at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:64)
        at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:70)
        at java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:266)
        at java.base/java.util.Objects.checkIndex(Objects.java:361)
        at java.base/java.util.ArrayList.get(ArrayList.java:427)
        at TestBed.main(TestBed.java:16) 

This code returns an error because i begins iterating at an index of 1. Therefore, when it attempts to execute intArray.get(3), it crashes. There is no value in the third index; the array only contains values for indexes 0, 1, and 2.