ArrayList类

它是一个引用 对象数组

package day18.demo01;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class demo01Iterator {
	public static void main(String[] args) {
		Collection<String> coll=new ArrayList<>();
		
		coll.add("第一");
		coll.add("第二");
		coll.add("第三");
		coll.add("第四");
		coll.add("第五");
		coll.add("第六");
		
		Iterator<String> it=coll.iterator();
		if(it.hasNext()) {
			String e=it.next();
			System.out.println(e);
		}
		if(it.hasNext()) {
			String e=it.next();
			System.out.println(e);
		}
		System.out.println("======================");
		while(it.hasNext()) {
			String e=it.next();
			System.out.println(e);
		}
		System.out.println("======================");
		for(Iterator<String> it2=coll.iterator();it2.hasNext();) {
			String e=it2.next();
			System.out.println(e);
		}
		System.out.println("========第三次========");
		for(String s:coll) {
			System.out.println(s);
		}
		System.out.println("========第四次========");
		int[] arr1= {77,3,4,5,6,7};
		for(int i=0;i<arr1.length;i++) {
			System.out.println(i);
		}
		for(int i:arr1) {
			System.out.println(i);
		}
	}
}

package day18.demo01;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;

public class demo01Collection {
	public static void main(String[] args) {
		//ArrayList<String> coll01=new ArrayList<>();
		//Collection<String> coll02=new ArrayList<>();
		Collection<String> coll=new HashSet<>();
		System.out.println(coll);
		
		boolean b1=coll.add("张三");
		System.out.println(b1);
		System.out.println(coll);
		coll.add("李四");
		coll.add("李四");
		coll.add("王五");
		coll.add("赵六");
		System.out.println(coll);
		
		boolean b2=coll.remove("王五");
		System.out.println(b2);
		System.out.println(coll);
		
		boolean b3=coll.contains("赵六");
		System.out.println(b3);
		
		boolean b4=coll.contains("王五");
		System.out.println(b4);
		boolean b5=coll.isEmpty();
		System.out.println(b5);
		
		int b6=coll.size();
		System.out.println(b6);
		
		Object[] arr=coll.toArray();
		//for(int i=0;i<arr.length;i++) {
			System.out.println(arr[0]);
		//}
		
		System.out.println("========================");
		coll.clear();
		System.out.println(coll);
		b5=coll.isEmpty();
		System.out.println(b5);
	}
}

编译期异常和运行期异常

package day18.demo02;

import java.util.Date;
import java.text.ParseException;
import java.text.SimpleDateFormat;

public class demo02Exception {
	public static void main(String[] args) {
		//编译期异常
		SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
		
		Date date=null;
		try {
			date=sdf.parse("2021-05-11");
		}catch(ParseException e) {
			e.printStackTrace();
		}
		
		System.out.println(date);
		
		//runtimeException   运行期异常
		int[] arr= {1,2,3};
		System.out.println(arr[0]);
		try {
			System.out.println(arr[2]);
		}catch(Exception e) {
			System.out.println("第一句测试");
			System.out.println(e);
		}//error  错误
		int[] arr2=new int[1024*10241024*1024*1024*1024*1024];
		System.out.println("后续代码");
		
	}
}

package day18.demo02;

public class demo02Throw {
	public static void main(String[] args) {
		int[] arr=null;
		//int[] arr=new int[3];
		
		int e=getElement(arr,3);
		System.out.println(e);
	}


	private static int getElement(int[] arr, int index) {
		if(arr==null) {
			throw new NullPointerException("传递的数组值是NULL");
		}
		if(index<0||index>arr.length-1) {
			throw new ArrayIndexOutOfBoundsException("传递的索引超出了数组的正常使用范围");
		}
		int ele=arr[index];
		return 0;
	}
}

package day18.demo02;

import java.io.FileNotFoundException;
import java.io.IOException;

public class demo02Throws {
	//public static void main(String[] args) throws FileNotFoundException, IOException
	//public static void main(String[] args) throws IOException
	public static void main(String[] args) throws Exception {
		readFile("c:\\a.txt");
		//readFile("c:\\b.txt");     传递的文件不是c:\\a.txt
		//readFile("c:\\a");         文件后缀名有误
		//readFile("c:\\ba");        传递的文件不是c:\\a.txt
		System.out.println("后续代码");
	}
	
	private static void readFile(String fileName) throws FileNotFoundException,IOException {
		if(!fileName.equals("c:\\a.txt")) {
			throw new FileNotFoundException("传递的文件不是c:\\a.txt");
		}
		if(!fileName.endsWith(".txt")) {
			throw new IOException("文件后缀名有误");
		}
		System.out.println("文件正确");
	}
	
}

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