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What is the difference between hashmap and concurrenthashmap

Difference: HashMap is thread-unsafe. When multi-threaded operations occur, security risks may arise; ConcurrentHashMap is thread-safe. ?HashMap does not support concurrent operations and has no synchronization method; ConcurrentHashMap supports concurrent operations.

Feb 02, 2021 am 11:14 AM

concurrenthashmap hashmap java

JVM learning Java memory structure

The full name of JVM is Java Virtual Machine-the running environment of java program (the running environment of java binary bytecode)

Feb 01, 2021 pm 05:41 PM

What are the three objects of the event processing model?

The three objects of the event processing model: 1. Event source; the place where the event occurs is usually each component. 2. Events; encapsulate specific things that happen on interface components. 3. Event listener: Responsible for monitoring events that occur in event sources and responding accordingly to various events.

Jan 28, 2021 pm 04:54 PM

What are the java loop statements?

Java loop statements: 1. while loop, code is [while (judgment condition) {loop body (one or more statements)}]; 2. do while loop, code is [do{loop body}]; 3. for loop , the code is [for (declaration of loop increment; judgment condition; increment auto-increment) {loop body}].

Jan 26, 2021 pm 05:12 PM

java loop statement

What are the four commonly used frameworks for java development?

There are four commonly used frameworks for Java development: 1. Struts is an MVC framework based on the Sun Java EE platform; 2. Spring is a lightweight Java EE application framework; 3. Hibernate is an open source object-relational mapping framework; 4. , Swing graphical user interface library.

Jan 26, 2021 pm 02:21 PM

java development

How to open jar file

How to open the jar file: first download and install java jdk, open the Java file; then click on the [.jar] file and select the opening method as Java; finally, after installation, click to decompress to "XXX(E)".

Jan 26, 2021 pm 01:49 PM

jar file

How to read excel table information in java

How to read excel table information in java: 1. Get the excel table file to be read through the [Workbook.getWorkbook(new File("E://excel.xls"));] code; 2. [book.getSheet( 0);] Get table information.

Jan 22, 2021 pm 03:18 PM

java

Calculate how to calculate date and time difference in Java8

The java basic tutorial column introduces how to calculate the date and time difference in Java 8. The method is simple and concise. Friends in need can take a look for reference.

Jan 19, 2021 am 09:34 AM

java8

You must know the difference between '==' and equals() in java

Today we will discuss the difference between "==" and equals() in Java ==: The relational operator compares whether the contents of two values ????are equal in basic data types, and compares whether the addresses of two objects are equal in reference types. Equality equals() is a method in the Object class

Jan 18, 2021 pm 05:20 PM

equals() java

What are the java middleware technologies?

Java middleware technologies include: 1. tomcat; 2. Weblogic; 3. JBOSS; 4. Coldfusion; 5. Websphere; 6. GlassFish.

Jan 13, 2021 pm 05:08 PM

java middleware

what are java features

Java features: 1. Cross-platform; 2. Security; 3. Object-oriented; 4. Simplicity; 5. High performance; 6. Distributed; 7. Multi-threading, which can bring better interactive response and real-time behavior; 8. Robustness.

Jan 12, 2021 pm 04:51 PM

Java Features

What is the role of volatile in java

The role of volatile in java: 1. Java provides the volatile keyword to ensure visibility; 2. To ensure orderliness, the code is [context = loadContext(); inited = true;]; 3. Provide double check.

Jan 11, 2021 am 11:13 AM

java volatile

What are the java member variables?

Java member variables include: 1. Instance variables [String id, private String colorType]; 2. Class variables [private static String depart]; 3. Constants [final String design=yang].

Jan 11, 2021 am 10:10 AM

java Member variables

How to calculate date time difference in Java8

The java basic tutorial column introduces how to calculate the date and time difference in Java 8. The method is concise. Friends in need can take a look, summarize and learn, or discuss together.

Jan 07, 2021 pm 06:06 PM

java8