Java 示例代码笔记(遗忘点)

1.trim()

Scanner scanner=new Scanner(System.in);

String s=scanner.nextLine();

//s=" SherlyHan "

s.trim();

//s="SherlyHan"  去掉String首尾的空格

2.常见类型转换

(1)String->int

int s1=Integer.parseInt(string);

int s1=Integer.valueOf(string).intValue();

//int s1=Integer.valueOf(string);也是对的

(2)int->String

int i=1;

String s=String.valueOf(i);//int i不被初始化，String 不能进行强制转换

String s=Integer.toString(i);

Stirng s=""+i;

(3.1)String->Integer

Integer integer=Integer.valueOf(string);

(3.2)Integer->String

Integer inte;

String s=inte.toString();

(4)Integer类->int变量名

int i=integer.intValue();

(5)int->Integer

int i;

Integer integer=new Integer(i);

(6)String->char

String s;

char[] ch=s.toCharArray();

ch.get(0);//只有一个char时

(7)char->String

String s=ch.toString();

3.

判断String是否相等：string.equals(S);

4.IO

(1)FileOutputStream out=new FileOutputStream(file);

out.write(string.getBytes());

(2)FileInputStream in=new FileInputStream(file);

int i=in.read();

while(i!=-1)

{
//得到的是编码

i=in.read();

}

(3)BufferedReader br=new BufferedReader(new FileReader(f));

String line;

whie((line=br.readLine()) != null)

　　System.out.println(line);

(4)DataOutputStream dos=new DataOutputStream(new FileOutputStream(f));

dos.writeInt(string.gertBytes().length);

 

DataInputStream dis=new DataInputStream(new FileInputStream(f));

byte[] buf=new byte[100];

int len=dis.readInt();

dis.read(buf,0,len);

(5)ObjectOutputStream oos=new ObjectOutputStream(new FileOutputStream(f));

oos.writeobject(al.get(i));//ArrayList<type> al=new ArrayList();

ObjectInputStream ois=new ObjectInputStream9new FileInputStream(f));

object=(type)ois.readObject();//强制类型转化

5.collection

HashMap.containsKey(key);

6.抽象类

abstract calss Myclass<T>{

protected abstract T peek();

}