前言
本期任务:毕向东老师Java视频教程学习笔记(共计25天)
原视频链接:黑马程序员_毕向东_Java基础视频教程day01:编写HelloWorld程序day02:操作符与条件选择语句day03:循环语句与函数day04:数组day07:继承、抽象类与接口day08:多态day09:异常处理day11:多线程day12:线程安全与同步机制day13:String类day14:集合(ArrayList,LinkedList,HashSet)day15:集合(TreeSet)和泛型)day16:集合(HashMap、TreeMap)day17:集合框架的工具类(Arrays、Collections)day18:IO流(字符流读写)day19:IO流(字节流、转换流读写)day20:IO流(File对象)
代码
import java
.util
.*
;
public class ArraysDemo {
public static void main(String
[] args
) {
Integer
[] arr
= {1, 2, 3};
System
.out
.println(Arrays
.toString(arr
));
List
<Integer> list
= Arrays
.asList(arr
);
System
.out
.println("contians: "+list
.contains(2));
}
}
import java
.util
.*
;
class MyComparator implements Comparator<String> {
public int compare(String s1
, String s2
) {
int num
= ((Integer
) s1
.length()).compareTo((Integer
) s2
.length());
if (num
== 0) {
return s1
.compareTo(s2
);
}
return num
;
}
}
public class CollectionsDemo {
public static void main(String
[] args
) {
List
<String> list
= new ArrayList<String>();
list
.add("abcd");
list
.add("aaa");
list
.add("ggda");
list
.add("dafsf da");
list
.add("dafdfae");
System
.out
.println("未排序:\r\n" + list
);
System
.out
.println("最大值:"+Collections
.max(list
));
System
.out
.println("最小值:"+Collections
.min(list
));
Collections
.sort(list
);
System
.out
.println("按字母表顺序:\r\n" + list
);
Collections
.sort(list
, new MyComparator());
System
.out
.println("最长元素:"+Collections
.max(list
, new MyComparator()));
System
.out
.println("最短元素:"+Collections
.min(list
, new MyComparator()));
System
.out
.println("按长度排序:\r\n" + list
);
}
}
import java
.util
.*
;
public class CollectionToArray {
public static void main(String
[] args
) {
ArrayList
<String> al
= new ArrayList<String>();
al
.add("dkajlf");
al
.add("daf");
al
.add("ddaaf");
al
.add("gafsg");
String
[] arr
= al
.toArray(new String[al
.size()]);
System
.out
.println(arr
);
System
.out
.println(Arrays
.toString(arr
));
}
}
import java
.util
.*
;
public class ForEachDemo {
public static void main(String
[] args
) {
ArrayList
<String> al
= new ArrayList<String>();
al
.add("dalkfj;");
al
.add("adf;");
al
.add("gasg;");
for (String s
: al
) {
System
.out
.println(s
);
}
System
.out
.println(al
);
int[] arr
= {1, 2, 3, 4, 5};
for (int i
: arr
) {
System
.out
.println(i
);
}
HashMap
<Integer, String> hm
= new HashMap<Integer, String>();
hm
.put(1, "a");
hm
.put(2, "b");
hm
.put(3, "c");
for (Map
.Entry
<Integer, String> me
: hm
.entrySet()) {
System
.out
.println(me
.getKey() + "::" + me
.getValue());
}
}
}
public class ParamMethodDemo {
public static void main(String
[] args
) {
show("haha", 2, 3, 4, 6, 7);
}
public static void show(String str
, int... arr
) {
System
.out
.println(arr
.length
);
}
}