Java – Basics

``` Explanation of Terms In-Place Algorithm（原地算法）: an in-place algorithm is an algorithm which transforms input using no auxiliary data structure. However a small amount of extra storage space is allowed for auxiliary variables. The input is usually overwritten by the output as the algorithm executes. In-place algorithm updates input sequence only through replacement or swapping of elements. (Wikipedia) Basic Knowledge Character Class https://www.tutorialspoint.co... https://docs.oracle.com/javas... Integer to String Convert using Integer.toString(int) Convert using String.valueOf(int) To Declare an ArrayList with Values For example List<String> temp = new ArrayList<String>(Arrays.asList("1", "12")); Iterate through a HashMap https://stackoverflow.com/que... If you're only interested in the keys, you can iterate through the keySet() of the map: Map<Object, Object> map = ...; for (Object key : map.keySet()) { // ... } If you only need the values, use values(): for (Object value : map.values()) { // ... } Finally, if you want both the key and value, use entrySet(): for (Map.Entry<Object, Object> entry : map.entrySet()) { Object key = entry.getKey(); Object value = entry.getValue(); // ... } Coding Test i++ & ++i 赋值 public class test { public static void main(String[] args) { int i1=0, i2=0, i3=0, i4=0, index1=0, index2=0, index3=0, index4=0; int[] num1 = new int[10]; int[] num2 = new int[10]; int[] num3 = new int[10]; int[] num4 = new int[10]; while (index1 < 5 && index2 < 5 && index3 < 5 && index4 < 5) { num1[index1++] = i1++; //01234 num2[++index2] = i2++; //001234 num3[index3++] = ++i3; //12345 num4[++index4] = ++i4; //012345 } for (int n : num1) { System.out.print(n); } System.out.println(); for (int n : num2) { System.out.print(n); } System.out.println(); for (int n : num3) { System.out.print(n); } System.out.println(); for (int n : num4) { System.out.print(n); } } } /* Output * 0123400000 * 0012340000 * 1234500000 * 0123450000 */ 要写的 StringBuilder & StringBuffer Stack & Queue Hash Table & HashMap & HashSet Iterator ```