前言
大家好,今天给大家带来 详细讲解Java中的异常处理情况与I/O流的介绍以及类集合框架 的概述,希望你们喜欢
JAVA 异常
try…catch…finally结构的使用方法
class Test{public static void main(String args[]){ try{ int i = 1 / 0; } catch(Exception e){ e.printStackTrace(); } finally{ System.out.println("finally"); } System.out.println(5); } }class Test{public static void main(String args[]){ try{ Thread.sleep(1000); } catch(Exception e){ e.printStackTrace(); } } }
throw和throws的作用区别:
class Person{private int age;public void setAge(int age) throws Exception{ if(age<0){ RuntimeException e = new RuntimeException("年龄不能小于0"); throw e; } this.age = age; } }class Test{public static void main(String args[]){ Person person = new Person(); try{ person.setAge(-1); } catch(Exception e){ System.out.println(e); } } }
Error和Exception的区别
Error是Throwable的子类用于标记严重错误
Exception是Throwable的子类,指示合理的程序想去catch的条件,非严重错误。
try/catch的执行过程
如果出现异常,系统则会抛出一个异常,进行捕捉(catch操作),或在最后(finally)来进行处理。
throw和throws的区别
throws 出现在方法声明上,throw出现在方法体内。
异常分类
异常分类:可查异常,运行时异常和错误
说说IO
//第一种:输入流输出流//第二种:字节流字符流//第三种:节点流处理流//FileInputStreamclass Test{ public static void main(String args[]){
FileInputStream fis = null; try{
fis = new FileInputStream("e:/read.txt"); byte[] buffer = new byte[100];
fis.read(buffer,0,buffer. length ); for(int i = 0;i<buffer.length;i++){
System.out.println(buffer[i]);
}
} catch(Exception e){
System.out.println(e);
}
}
}
class Test{ public static void main(String args[]){ FileInputStream fis = null; FileOutputStream fos = null; try{ fis = new FileInputStream("e:/read.txt"); fos = new FileOutputStream("e:/write.txt"); byte[] buffer = new byte[100]; int temp = fis.read(buffer,0,buffer.length); fos.write(buffer,0,temp); } catch(Exception e){ System.out.println(e); } } }
class Test{ public static void main(String args[]){
FileInputStream fis = null;
FileOutputStream fos = null; try{
fis = new FileInputStream("e:/read.txt");
fos = new FileOutputStream("e:/write.txt"); byte[] buffer = new byte[1024]; while(true){ int temp = fis.read(buffer,o,buffer.length); if(temp = -1){ break;
}
fos.write(buffer,0,temp);
}
}catch(Exception e){
System.out.println(e);
}finally{ try{
fis. close ();
fos.close();
}catch(Excepiton e){
System.out.println(e);
}
}
}
}
//字符流public class TextChar public static void main(String args[]){ FileReader fr = null; FileWriter fw = null; try{ fr = new FileReader("e:/read.txt"); fw = new FileWriter("e:/write.txt"); char[] buffer = new char[100]; int temp = fr.read(buffer,0,buffer.length); fw.write(buffer,0,temp); } catch(Exception e){ System.out.println(e); }finally{ try{ fr.close(); fw.close(); } catch(Excepiton e){ System.out.println(e); } } }
//FileReader和BufferedReaderclass Test{ public static void main(String args[]){ FileReader fileReader = null; BufferedReader bufferedReader = null;try{ fileReader = new FileReader("e:/read.txt"); bufferedReader = new BufferedReader(fileReader); String line = null; while(true){ line = bufferedReader.readLine(); if(line == null){ break; } System.out.println(line); } }catch(Exception e){ System.out.println(e); } finally{ try{ bufferedReader.close(); fileReader.close(); } catch(Exception e){ System.out.println(e); } } } }
public class Test{ public static void main(String[] args) throws Exception{ //字节流 FileInputStream in = new FileInputStream("c:/read.txt"); FileOutStream out = new FileOutputStream("c:/write.txt"); byte[] buffer = new byte[1024]; int len; while( (len = in.read(buffer)) != -1){ out.write(buffer,0,len); } in.close(); out.close(); //字符流 BufferedReader bf = new BufferedReader(new FileReader("c:/read.txt"); BufferedWriter bw = new BufferedWriter(new FileWriter("c:/write.txt"); String str; while( (str=bf.readLine()) != null ){ bw.write(str); bw.newLine(); } bf.close(); bw.close(); } }
集合框架
一组类和接口,位于java.util包,主要用于存储和管理对象,主要分为三大类—集合,列表和映射。
什么是集合(Set)
集合中对象是没有顺序的,并且没有重复对象;
什么是列表(List)
集合中对象可以有重复的对象,可以按照顺序取,也可以指定取。
什么是映射(Map)
每一个元素包含一个键对象和一个值对象,键不可以重复,值可以重复。
类集框架主体结构
interface Iterator Collection ListIterator List Set MapLinkeList ArrayList HashSet SortedSet HashMap SortedMap LinkedHashSet TreeSet LinkedHashMap TreeMap Comparable Comparator Collections Arrays//arrayList默认10,可无限长,关于泛型public class Test{ public static void main(String args[]){ //ArrayList arrayList = new ArrayList(); ArrayList<String> arrayList = new ArrayList<String>(); arrayList.add("a"); arrayList.add("b"); arrayList.add("c"); //String s = arrayList.get(1); //System.out.println(s); for(int i=0;i<3;i++){ String s = arrayList.get(i); System.out.println(s); } } } 优化 public class Test{ public static void main(String args[]){ ArrayList<String> arrayList = new ArrayList<String>(); arrayList.add("a"); arrayList.add("b"); arrayList.add("c"); arrayList.add("d"); for(int i = 0; i<arrayList.size();i++){ String s = arrayList.get(i); System.out.println(s); } } }
类集框架
集合 无序 不可重复
列表 有序 可重复
映射
Set继承了Collection
public class Test{
public static void main(String args[]){ //HashSet<String> hashSet = new HashSet<String>();
//Set<String> set = new HashSet<String>();
//别管就是转,方便
Set<String> set = new HashSet<String>(); set.add("a"); set.add("b"); set.add("c"); set.add("d"); int i = set.size();
System.out.println(i);
}
}
不可以重复public class Test{
public static void main(String args[]){ //HashSet<String> hashSet = new HashSet<String>();
//Set<String> set = new HashSet<String>();
//别管就是转,方便
Set<String> set = new HashSet<String>();
boolean b1 = set.isEmpty();
System.out.println(b1); set.add("a"); set.add("b"); set.add("c"); set.add("d"); set.add("c");
boolean b2 = set.isEmpty();
System.out.println(b2);
int i = set.size();
System.out.println("clear之前的长度"+i); set.clear();
int j = set.size();
System.out.println(j);
}
}
取数据,迭代 iterate器 ( Iterator )public class Test{public static void main(String args[]){ //HashSet<String> hashSet = new HashSet<String>();
//Set<String> set = hashSet;
//Iterator <-- Collection <-- Set <-- HashSet
//hasNext() next()
Set<String> set = new HashSet<String>();
set.add("a"); set.add("b"); set.add("c"); set.add("d"); set.add("c");
Iterator<String> it = set.iterator();
boolean b1 = it.hasNext(); if(b1){
String s = it.next();
System.out.println(s);
}
boolean b2 = it.hasNext(); if(b2){
String s = it.next();
System.out.println(s);
}
}
}
迭代器的使用
it.hasNext();
还有没有下一个元素,如果这个游标后面有元素就返回true,否则,false;
it.next();
返回游标所指位置的下一个元素,取出,用hasNext()看有没有,next取
优化public class Test{public stattic void main(String args[]){
Set<String> set = new HashSet<String>();
set.add("a"); set.add("b"); set.add("c"); set.add("d"); set.add("c");
Iterator<String> it = set.iterator(); while(it.hasNext()){
String s = it.next();
System.out.println(s);
}
}
}
什么是映射(Map)
每一个元素包含一个键对象和一个值对象,键不可以重复,值可以重复。
public class Test{public static void main(String args[]){ HashMap<String,String> hasMap = new HashMap<String,String>(); Map<String,String> map = hasMap; map.put("1","a"); map.put("2","b"); map.put("3","c"); map.put("4","d"); int i = map.size(); System.out.println(i); } }public class Test{public static void main(String args[]){ HashMap<String,String> hasMap = new HashMap<String,String>(); Map<String,String> map = hasMap; map.put("1","a"); map.put("2","b"); map.put("3","c"); map.put("4","d"); map.put("3","e"); int i = map.size(); System.out.println(i); String s = map.get("3"); System.out.println(ss); } }
public class TestCollection { public static void main(String[] args) { List<Hero> heros = new ArrayList<Hero>(); for (int i = 0; i < 5; i++) { heros.add(new Hero("hero name " + i)); } for (int i = 0; i < heros.size(); i++) { Hero h = heros.get(i); System.out.println(h); } } }
总结
本文讲了详细讲解Java中的异常处理情况与I/O流的介绍以及类集合框架,如果您还有更好地理解,欢迎沟通定位:分享 Android & Java 知识点,有兴趣可以继续关注