4.2 For Loops

Similar to while loops, for loops run until a condition is false. Format of for loop below:

for (int i = 0; i < 5; i++) {
    System.out.println(i);
}

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Explanation

  • in the above for loop:
    • int i = 0 defines the iterating variable
    • i < 5 is the condition (once i < 5 is false, this loop breaks)
    • i++ is the incrementation of the iterating variable
    • System.out.println(i); is the body code that runs every time the loop iterates

For Each Loops:

  • Apart from iterating using an incrementing variable, you can also iterate through items in a list.

    Example of For Each loop below

int[] list = {1, 2, 3, 4, 5}; // any list
for (int item : list) { // for each item in the list, execute the body
    System.out.println(item); // body code
}

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#python version
array=[1, 2, 3, 4, 5]
for i in array:
    print(i)

Explanation:

  • in the above loop:
    • int item : list - this line is saying that for each item in the list, execute code below
    • System.out.println(num); - this line is the body code.

Fun For Loop Hack:

Create a program that iterates through a list of numbers (int_list = {0, 4, 51, 83, 92, 10, 123, 145}) using both a for loop and a for each loop, then split the numbers in the list into even/odd lists, and output them.

import java.util.ArrayList;
int[]int_list = {0, 4, 51, 83, 92, 10, 123, 145};
ArrayList<Integer>even= new ArrayList();
ArrayList<Integer>odd=new ArrayList();
for(int i=0;i<int_list.length;i++){
    if(int_list[i]%2==0){
        even.add(int_list[i]);
    }
    else{
        odd.add(int_list[i]);
    }
}
System.out.println(even);
System.out.println(odd);



// method 2
int[]int_list = {0, 4, 51, 83, 92, 10, 123, 145};
ArrayList<Integer>even1= new ArrayList();
ArrayList<Integer>odd1=new ArrayList();
for(int i:int_list){
    if(i%2==0){
        even1.add(i);
    }
    else{
        odd1.add(i);
    }
}
System.out.println(even1);
System.out.println(odd1);

[0, 4, 92, 10]
[51, 83, 123, 145]
[0, 4, 92, 10]
[51, 83, 123, 145]
2
15


Iteration: 0

Current Velocity: 2, 2