什么是插入排序算法？

package com.sanjula.java.algorithms.InsertionSort;

public class InsertionSort {
    /**
     * Sort method using insertion sort
     * @param arr - Integer array passed in 
     *            to be sorted
     **/
    public void sort(int arr[]){
        // Store the length of the array
        int n = arr.length;
        // For loop to iterate through each
        for (int i = 0; i < n; i++){
            // Storing current element to check correct position
            int key = arr[i];
            int j = i - 1;

            // Move element to correct position if 
            // condition is true
            while(j >= 0 && arr[j] > key){
                arr[j + 1] = arr[j];
                j = j - 1;
            }
            arr[j + 1] = key;
        }
    }

    /**
     * Print the array supplied
     * @param arr - Array passed
     * @param msg - Message to be printed
     **/
    public static void printArray(int arr[], String msg) {
        int length = arr.length;
        System.out.println(msg);
        for (int i = 0; i < length; i++) {
            System.out.print(arr[i] + " ");
        }
        System.out.println();
    }

    public static void main(String[] args) {
        // Initialize and declare the array arr
        int arr[] = {25, 12, 3, 1, 9, 15};
        // Create new instance of class InsertionSort
        InsertionSort insertionSort = new InsertionSort();

        printArray(arr, "Array before insertion sort");
        // Invoke the sort method, passing in the array arr
        insertionSort.sort(arr);
        // Print the sorted array
        printArray(arr, "Array after insertion sort");
    }
}