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

Integer to String

1. Convert using Integer.toString(int)
2. 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

1. StringBuilder & StringBuffer
2. Stack & Queue
3. Hash Table & HashMap & HashSet
4. Iterator