2019 Java Interview Questions Basics series 228 (3)

2019 Java Interview Basics series 228

Juejin. Cn/post / 684490…

51. Class ExampleA inherits Exception and class ExampleB inherits ExampleA.

try {
	throw new ExampleB("b")} catch (ExampleA e) {system.out.println ("ExampleA"); } catch (Exception e) {system.out.println ("Exception");
}Copy the code

class Annoyance extends Exception {
}
class Sneeze extends Annoyance {
}
class Human {
	public static void main(String[] args)
	throws Exception {
		try {
			try {
				throw new Sneeze();
			}
			catch ( Annoyance a ) {
				System.out.println("Caught Annoyance");
				throw a;
			}
		}
		catch ( Sneeze s ) {
			System.out.println("Caught Sneeze");
			return ;
		}
		finally {
			System.out.println("Hello World!"); }}}Copy the code

Do List, Set, Map inherit from Collection interface?

53. Explain the storage performance and features of ArrayList, Vector and LinkedList.

What is the difference between Collections and Collections?

55, What are the characteristics of the List, Map, and Set interfaces when accessing elements?

56. How do TreeMap and TreeSet compare elements when sorting? How does the sort() method in the Collections utility class compare elements?

57, What is the difference between Thread’s sleep() and object’s wait() methods, which suspend execution?

What’s the difference between the sleep() method and the yield() method?

59. When A thread enters the synchronized method A of an object, can other threads enter the synchronized method B of that object?

Describe methods related to thread synchronization and thread scheduling.

How many ways to write multithreaded programs?

62, Synchronized?

63. Give examples of synchronization and asynchrony.

64. Do I call the run() or start() method to start a thread?

What is a thread pool?

What is the basic state of the thread and the relationship between the states?

67, briefly synchronized and Java. Util. Concurrent. The locks. The similarities and differences of the Lock?

68. How serialization is implemented in Java, and what does it mean?

How many types of flows are there in Java?

Write a method that enters a file name and a string and counts the number of times the string appears in the file.

import java.io.BufferedReader; import java.io.FileReader; Public final class MyUtil {// Methods in utility classes are accessed statically so keeping constructors private does not allow object creation (absolutely good practice) privateMyUtil() { throw new AssertionError(); } /** * count the number of occurrences of a given string in a given file ** @param filename filename * @param word string * @return*/ public static int countWordInFile(String filename, String word) {int counter = 0; try (FileReader fr = new FileReader(filename)) { try (BufferedReader br = new BufferedReader(fr)) { String line = null;while((line = br.readLine()) ! = null) { int index = -1;while (line.length() >= word.length() && (index =
					line.indexOf(word)) >= 0) {
						counter++;
						line = line.substring(index + word.length());
					}
				}
			}
		}
		catch (Exception ex) {
			ex.printStackTrace();
		}
		returncounter; }}Copy the code

71, How to use Java code to list all files in a directory?

import java.io.File;
class Test12 {
	public static void main(String[] args) {
		File f = new File("/Users/Hao/Downloads");
		for (File temp : f.listFiles()) {
			if(temp.isFile()) { System.out.println(temp.getName()); }}}}Copy the code

import java.io.File;
class Test12 {
	public static void main(String[] args) {
		showDirectory(new File("/Users/Hao/Downloads"));
	}
	public static void showDirectory(File f) {
		_walkDirectory(f, 0);
	}
	private static void _walkDirectory(File f, int level) {
		if(f.isDirectory()) {
			for(File temp : f.listFiles()) { _walkDirectory(temp, level + 1); }}else {
			for (int i = 0; i < level - 1; i++) {
				System.out.print("t"); } System.out.println(f.getName()); }}}Copy the code

class ShowFileTest {
	public static void main(String[] args) throws IOException {
		Path initPath = Paths.get("/Users/Hao/Downloads");
		Files.walkFileTree(initPath, new SimpleFileVisitor<Path>() {
			@Override
			public FileVisitResult visitFile(Path file, BasicFileAttributes
			attrs)
			throws IOException {
				System.out.println(file.getFileName().toString());
				returnFileVisitResult.CONTINUE; }}); }}Copy the code

Using Java socket programming to achieve a multithreaded echo server.

73. How many forms does an XML document definition take? What are the essential differences between them? What are some ways to parse AN XML document?

74. Where did you use XML in your project?

75, describe the steps of JDBC database operation.

Class.forName("oracle.jdbc.driver.OracleDriver");Copy the code

Connection con =
DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl"."scott"."tiger");Copy the code

PreparedStatement ps = con.prepareStatement("select * from emp
where sal between ? and ?");
ps.setint(1, 1000);
ps.setint(2, 3000);Copy the code

ResultSet rs = ps.executeQuery();Copy the code

while(rs.next()) {
	System.out.println(rs.getint("empno") + "-" +
	rs.getString("ename"));
}Copy the code

finally {
	if(con ! = null) { try { con.close(); } catch (SQLException e) { e.printStackTrace(); }}}Copy the code

76. What is the difference between a Statement and PreparedStatement? Which has better performance?

When using JDBC to operate database, how to improve the performance of reading data? How to improve the performance of updated data?

78, What is the role of connection pool in database programming?

What is the DAO pattern?

What is transaction ACID?

How do transactions occur in JDBC?

Can JDBC handle BLOBs and CLOBs?

83. Briefly describe regular expressions and their uses.

84. How are regular expression operations supported in Java?

import java.util.regex.Matcher;
import java.util.regex.Pattern;
class RegExpTest {
	public static void main(String[] args) {
		String str = "Beijing (Chaoyang District)(Xicheng District)(Haidian District)";
		Pattern p = Pattern.compile(". *? (? = \ ()");
		Matcher m = p.matcher(str);
		if(m.find()) { System.out.println(m.group()); }}}Copy the code

What are the ways to get a class object of a class?

How do I create objects with reflection?

How do I get and set the value of an object’s private field by reflection?

How do I call a method on an object through reflection?

import java.lang.reflect.Method;
class MethodInvokeTest {
	public static void main(String[] args) throws Exception {
		String str = "hello";
		Method m = str.getClass().getMethod("toUpperCase");
		System.out.println(m.invoke(str));
		// HELLO
	}
}Copy the code

89. Briefly describe the “six principles and one Law” of object orientation.

90. Briefly describe the design patterns you understand.

Write a singleton class in Java.

public class Singleton {
	private Singleton(){
	}
	private static Singleton instance = new Singleton();
	public static Singleton getInstance() {returninstance; }}Copy the code

public class Singleton {
	private static Singleton instance = null;
	private Singleton() {
	}
	public static synchronized Singleton getInstance() {if (instance == null) instance ＝ new Singleton();
		returninstance; }}Copy the code

What is UML?

What diagrams are commonly used in UML?

Write a bubble sort in Java.

import java.util.Comparator; /** * collator interface (policy mode: Encapsulate algorithms into separate classes with common interfaces so that they are interchangeable) * @author Luo hao ** / public interface Sorter {/** ** sort * @param list array to sort */ public <T extends Comparable<T>> void sort(T[] list); Public <T> void sort(T[] list, Comparator<T> comp); } import java.util.Comparator; Public class BubbleSorter implements Sorter {@override public <T category <T>> void sort(T[] list) { Boolean swapped =true;
		for (int i = 1, len = list.length; i < len && swapped; ++i) {
			swapped = false;
			for (int j = 0; j < len - i; ++j) {
				if (list[j].compareTo(list[j + 1]) > 0) {
					T temp = list[j];
					list[j] = list[j + 1];
					list[j + 1] = temp;
					swapped = true;
				}
			}
		}
	}
	@Override
	public <T> void sort(T[] list, Comparator<T> comp) {
		Boolean swapped = true;
		for (int i = 1, len = list.length; i < len && swapped; ++i) {
			swapped = false;
			for (int j = 0; j < len - i; ++j) {
				if (comp.compare(list[j], list[j + 1]) > 0) {
					T temp = list[j];
					list[j] = list[j + 1];
					list[j + 1] = temp;
					swapped = true;
				}
			}
		}
	}
}Copy the code

Write a half search in Java.

import java.util.Comparator;
public class MyUtil {
	public static <T extends Comparable<T>> int binarySearch(T[] x, T
	key) {
		returnbinarySearch(x, 0, x.length- 1, key); } public static <T> int binarySearch(T[] x, T key, Comparator<T> comp) {int low = 0; int high = x.length - 1;while (low <= high) {
			int mid = (low + high) >>> 1;
			int cmp = comp.compare(x[mid], key);
			if (cmp < 0) {
				low= mid + 1;
			} else if (cmp > 0) {
				high= mid - 1;
			} else {
				returnmid; }}return- 1; } private static<T extends Comparable<T>> int binarySearch(T[] x, int low, int high, T key) {if(low <= high) {
			int mid = low + ((high -low) >> 1);
			if(key.compareTo(x[mid])== 0) {
				return mid;
			} else if(key.compareTo(x[mid])< 0) {
				return binarySearch(x,low, mid - 1, key);
			} else {
				returnbinarySearch(x,mid + 1, high, key); }}return -1;
	}
}Copy the code

The last