Java 笔记

ArrayList<String> List = new ArrayList<String>(); //定义动态数组
List.add(temp); //添加字符串


List<Integer> ret = new ArrayList<Integer>();
ret.add(i+1);

String.Trim 方法
·Trim()    从当前 String 对象移除所有前导空白字符和尾部空白字符。

java.lang.string.split 
split 方法 
将一个字符串分割为子字符串，然后将结果作为字符串数组返回。

String[] res = s.trim().split("\\s+"); 将头尾空格去掉，并且切割成单词

sb.append(res[i]).append(" "); //每次添加 单词+“ ” 组合

return sb.toString().trim(); //将字符串头尾空格去掉 

arr.insert(0,(char)(‘A‘+n%26));

 1 十进制转成十六进制： 
 2 Integer.toHexString(int i) 
 3 十进制转成八进制 
 4 Integer.toOctalString(int i) 
 5 十进制转成二进制 
 6 Integer.toBinaryString(int i) 
 7 十六进制转成十进制 
 8 Integer.valueOf("FFFF",16).toString() 
 9 八进制转成十进制 
10 Integer.valueOf("876",8).toString() 
11 二进制转十进制 
12 Integer.valueOf("0101",2).toString() 

· Arrays.sort(nums);

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Main{
public static void print(int index ,Object obj){
System.out.println(String.format("{%d},%s",index,obj.toString()));
}

public static void main(String[] args){
//demoString();
demoList();
}

public static void demoList(){
List<String> strList=new ArrayList<String>();
for(int i=0;i<4;i++){
strList.add(String.valueOf(i));
}
print(1,strList);

List<String> strListB=new ArrayList<String>();
for(int i=0;i<4;i++){
strListB.add(String.valueOf(i*i));
}
strList.addAll(strListB);
print(2,strList);
strList.remove(0);
print(3,strList);
strList.remove(String.valueOf(1));
print(4,strList);
print(5,strList.get(1));

Collections.sort(strList);
print(6,strList);
Collections.sort(strList, new Comparator<String>() {
@Override
public int compare(String o1, String o2) {
return o2.compareTo(o1);
}
});
print(7,strList);
}
/*
{1},[0, 1, 2, 3]
{2},[0, 1, 2, 3, 0, 1, 4, 9]
{3},[1, 2, 3, 0, 1, 4, 9]
{4},[2, 3, 0, 1, 4, 9]
{5},3
{6},[0, 1, 2, 3, 4, 9]
{7},[9, 4, 3, 2, 1, 0]
*/

public static void demoString(){
String str="Hello nowcoder";
print(1,"Hello!");
print(2,str.charAt(6));
print(3,str.codePointAt(1));
print(4,str.compareTo("Hello mewcoder"));
print(5,str.compareTo("Hello pewcoder"));
print(6,str.contains("Hello"));
print(7,str.indexOf(‘e‘));
print(8,str.compareToIgnoreCase("Hello Nowcoder"));
print(9,str.concat("!!"));
print(10,str.endsWith("nowcoder"));
print(11,str.startsWith("Hello"));
print(12,str.lastIndexOf(‘o‘));
print(13,str.toUpperCase());
print(14,str.replace(‘o‘,‘a‘));
print(15,str.replaceAll("o|l","a"));
print(16,str.replaceAll("Hello","hi"));

StringBuilder sb =new StringBuilder();
sb.append(true);
sb.append(1);
sb.append(2.2);
print(17,sb.toString());
print(18,"a"+"b"+String.valueOf(12));
}
/*{1},Hello!
{2},n
{3},101
{4},1
{5},-2
{6},true
{7},1
{8},0
{9},Hello nowcoder!!
{10},true
{11},true
{12},10
{13},HELLO NOWCODER
{14},Hella nawcader
{15},Heaaa nawcader
{16},hi nowcoder
{17},true12.2
{18},ab12
*/
}

List<Integer> array = Arrays.asList(new Integer[]{1,2,3,4,5});
Collections.shuffle(array);