1、版本控制系統：人人網，支付寶等用的都是svn;可以用： github, bitBucket等等。
2、封裝（實現接口）、繼承（繼承類）、多態（在類中對已有實現重新實現）。
3、Set、List、Map、Random、Date、Math
public static void myPrint(int index, Object object) {
System.out.println(String.format("{%d} %s", index, object.toString()));
}
public static void demoControlFlow() {
int score = 60;
if (score > 80) {
myPrint(1, "A");
} else if (score > 60) {
myPrint(2, "B");
} else {
myPrint(3, "C");
}
String grade = "B";
switch (grade) {
case "A":
myPrint(11, "better than B");
break;
case "B":
myPrint(12, "is B");
break;
case "C":
myPrint(13, "worse than B");
break;
default:
myPrint(15, "not one");
}
for (int i = 0; i <= 4; ++i) {
if (i == 1) continue;
if (i == 3) break;
myPrint(21, "loop");
myPrint(31, i);
}
String str = "Hello world";
for (char c : str.toCharArray()) {
myPrint(41, c);
}
}
public static void demoString() {
String str = "Liuzewei is a greatful man";
myPrint(1, str.indexOf('a'));
myPrint(2, str.charAt(12));
myPrint(3, str.codePointAt(12));
myPrint(4, str.compareTo("uESTC"));
myPrint(5, str.compareTo("Liuzewei is e greatful man"));
myPrint(6, str.compareTo("liuzewei is a greatful man"));
myPrint(7, str.compareToIgnoreCase("liuzewei is a greatful man"));
myPrint(8, str.contains("s"));
myPrint(9, str.concat(" \r\n Yes"));
myPrint(10, str.startsWith("Liu"));
myPrint(11, str.codePointBefore(2));
myPrint(11, str.codePointCount(1, 2));
myPrint(12, str.lastIndexOf('a'));
myPrint(13, str.replace('a', 'e'));
myPrint(14, str.replaceAll("a|L", "e"));
StringBuilder strb = new StringBuilder();
strb.append(true);
strb.append(1);
strb.append(2.2);
myPrint(15, strb.toString());
}
public static void demoList() {
List<String> strList = new ArrayList<String>();//ArrayList非常常用
for (int i = 0; i < 4; i++) {
strList.add(String.valueOf(i));
}
myPrint(1, strList);
List<String> strListB = new ArrayList<String>();
for (int i = 5; i < 7; i++) {
strListB.add(String.valueOf(i));
}
myPrint(2, strListB);
strListB.addAll(strList);
myPrint(3, strListB);
strListB.remove(0);
myPrint(4, strListB);
strListB.remove(String.valueOf(6));
myPrint(5, strListB);
myPrint(6, strListB.get(3));
strListB.add("12");
strListB.add(String.valueOf(15));
Collections.sort(strListB);
myPrint(7, strListB);
/**
* 首字母順序排序
*/
Collections.sort(strListB, new Comparator<String>() {
@Override
public int compare(String o1, String o2) {
return o2.compareTo(o1);
}
});
myPrint(8, strListB);
Collections.reverse(strListB);
myPrint(9, strListB);
int[] array = new int[]{1, 2, 3};//用的少一些
myPrint(10, array[2]);
}
@Test
public void demoSet() {
Set<String> strSet = new HashSet<String>();//集合中元素不重複
for (int i = 0; i < 3; i++) {
strSet.add(String.valueOf(i));
strSet.add(String.valueOf(i));
strSet.add(String.valueOf(i));
}
myPrint(1, strSet);
strSet.remove("1");
myPrint(2, strSet);
strSet.contains("4");
myPrint(3, strSet.contains("4"));
strSet.addAll(Arrays.asList(new String[]{"12", "13", "14", "15"}));
myPrint(4, strSet);
for (String value : strSet) {
myPrint(5, value);
}
myPrint(6, strSet.isEmpty());
myPrint(7, strSet.size());
}
@Test
public void demoKeyValue() {
System.out.println(5/2);
Map<String, String> map = new HashMap<>();
for (int i = 0; i < 4; i++) {
map.put(String.valueOf(i), String.valueOf(i * i));
}
myPrint(1, map);
map.entrySet().forEach(i->myPrint(8, i.getKey() + ":" + i.getValue()));
map.entrySet().stream().forEach(i-> System.out.println(i.getKey()));
for (Map.Entry<String, String> entry : map.entrySet()) {
myPrint(2, entry.getKey() + ":" + entry.getValue());
}
myPrint(3, map.keySet());
myPrint(4, map.values());
myPrint(5, map.containsValue("4"));
myPrint(6, map.get("2"));
map.replace("1", "A");
myPrint(7, map);
}
@Test
public void demoException1() {
try {
myPrint(1, "hello");
String a = null;
a.indexOf('a');
myPrint(4, a);
int b = 2;
b = b / 0;
String c = null;
c.indexOf("c");
} catch (NullPointerException npe) {
myPrint(3, "null");
} catch (Exception e) {
myPrint(5, "error");
} finally {
//做清理工作
myPrint(2, "end1");
}
}
@Test
public void demoException() throws Exception {
myPrint(1, "hello");
String a = "e";
a.indexOf('e');
myPrint(4, a);
int b = 2;
if(b == 2){
throw new Exception("我故意的");
}
b = b / 0;
String c = null;
c.indexOf("c");
}
@Test
public void demoCommon() {
Random random = new Random();//實際上是僞隨機數
random.setSeed(1); //初始seed設定後，刷新隨機函數不會改變值
for (int i = 0; i < 4; i++) {
myPrint(1, random.nextInt(100));
myPrint(2, random.nextDouble());
}
List<Integer> array = Arrays.asList(new Integer[]{1, 2, 3, 8, 9});
myPrint(3, array);
Collections.shuffle(array);
myPrint(4, array);
Date data = new Date();
myPrint(5, data.getTime());
myPrint(6, data);
DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
DateFormat df2 = new SimpleDateFormat("y.M.d");
myPrint(6, df.format(data));
myPrint(8, df2.format(data));
myPrint(7, df);
myPrint(9, DateFormat.getDateInstance(DateFormat.SHORT).format(data));
myPrint(10, UUID.randomUUID());
myPrint(11, Math.ceil(1.1));//向上進位
myPrint(12, Math.floor(5.8));//去除小數點，保留整數
}
public static void demoClass() {
Animal animal = new Animal("Jim", 2);
animal.say();
animal = new Human("Bob",24,"China");
animal.say();
}
@Test
public void exercise(){
Random random = new Random();
random.setSeed(1);
System.out.println(random.nextInt(100));
}
public static Animal getAnimal(int type){
return new Human("LIu",25,"Jape");
}
public static void main(String[] args) {
// demoControlFlow();
// stringDemo();
// demoString();
// demoList();
// demoSet();
// demoKeyValue();
// demoException1();
// demoCommon();
demoClass();
}