4.4 Array Traversals

1. Exam Points

• Traverse an array using for loops (use indexes).
• Traverse an array using while loops (use indexes).
• Traverse an array using for-each loops (not use indexes).
• Assigning a new value to the enhanced for loop variable does not change the value stored in the array (applys to arrays storing primitive values).
• Traverse part of the elements of an array. (index += 2, etc.)

2. Knowledge Points

(1) Traverse Arrays

• Traversing an array is when repetition statements (loop) are used to access all or some of the elements in an array.
• Loops commonly used for array traversals.
  • for loops (use indexes)
  • while loops (use indexes)
  • for-each loops, i.e, enhanced for loops (no use of indexes)
• Traverse an 1D array of primitive values.
  • Example:
    

    int[] nums = { 1, 2, 3, 4 };
    // 1. for loop (use indexes)
    for (int i = 0; i < nums.length; i++) { 
        // i is an index, nums[i] is an element
        System.out.print(nums[i] + " ");
    }
    
    System.out.println();
    
    // 2. while loop (use indexes)
    int j = 0;
    while(j < nums.length ){
        // j is an index, nums[j] is an element
        System.out.print(nums[j] + " ");
        j++;
    }
    
    System.out.println();
    
    System.out.println();
    // 3. for-each loop (no use of indexes)
    for (int x : nums) { // here type 'int' follows the type of the array
        // here x is the current element
        System.out.print(x + " ");
    }
    

• Traverse an 1D array of object references.
  • Example:
    

    class Pig {
        
        private String name;
        private boolean vaccinated;
        
        public Pig(String n, boolean v) {
            name = n;
            vaccinated = v;
        }
        
        public String getName() {
            return name;
        }
        
        public boolean isVaccinated() {
            return vaccinated;
        }
    }
    

    // 1. use for loops
    for (int i = 0; i < pigs.length; i++) {
        System.out.println(pigs[i].getName() + "-" + pigs[i].isVaccinated());
    }
    
    // 2. use for-each loops
    for (Pig p : pigs) {
        System.out.println(p.getName() + "-" + p.isVaccinated());
    }
    

3. Exercises

• Practice
• Solution