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How to convert an ArrayList to an array in Java

To convert an ArrayList to an array, you need to select a method according to the object or the original type: 1. Use list.toArray(newType[0]) to get an array of objects of the specified type, such as String[]; 2. Avoid casting the result toArray() to avoid throwing ClassCastException; 3. For original arrays such as int[], you need to manually convert them through streams or loops, such as list.stream().mapToInt(Integer::intValue).toArray(). The correct method depends on the data type. It is recommended toArray(newT[0]) for object arrays, original

Aug 11, 2025 pm 07:46 PM

java

How to use CountDownLatch in Java

CountDownLatch is used to make one or more threads wait for other threads to complete operations. 1. Set counts during initialization; 2. The worker thread calls countDown() to decrement count; 3. The coordinated thread calls await() to wait for the count to return to zero; 4. After the count is zero, all waiting threads are released and cannot be reused. It is suitable for scenarios where multitasking is completed or threads are started synchronously.

Aug 11, 2025 pm 07:37 PM

How to replace a character in a string in Java?

Usethereplace()methodtoreplacealloccurrencesofacharacter,asitissimple,safe,andefficientformostcases;2.AvoidreplaceAll()forsinglecharacterssinceitusesregexandcanbeerror-prone;3.UseStringBuilderformultipleorperformance-sensitivemodificationsduetoitsmut

Aug 11, 2025 pm 07:36 PM

Java Properties file: Flexible access to configuration values through partial key names

In view of the scenario where Java Properties files cannot directly obtain values through partial key names after loading, this article introduces a practical solution. By traversing all attribute keys and using string matching methods, you can flexibly locate the required value according to the substring of the key, thereby meeting the search needs of incomplete matching, especially when the key name contains multiple logical segments.

Aug 11, 2025 pm 07:27 PM

What is a HashMap in Java?

AHashMapinJavaisadatastructurethatstoreskey-valuepairsforefficientretrieval,insertion,anddeletion.Itusesthekey’shashCode()methodtodeterminestoragelocationandallowsaverageO(1)timecomplexityforget()andput()operations.Itisunordered,permitsonenullkeyandm

Aug 11, 2025 pm 07:24 PM

java hashmap

Java extracts substrings between the beginning and end vowels in a string

This article aims to provide a simple and efficient Java method for extracting substrings from the first vowel to the last vowel in a string. By using regular expressions, lengthy loops and conditional judgments can be avoided, simplifying the code and reducing the possibility of errors. This article will introduce the method in detail and provide sample code and considerations.

Aug 11, 2025 pm 07:15 PM

Generate an arithmetic sequence so that its sum is the specified value, and the first item is the specified value

This article introduces an algorithm that can generate a sequence with the sum of 100 (configurable) and the first item is a user-specified value. The core idea of the algorithm is to subtract the sum from the first term, then calculate the arithmetic sequence of the remaining terms, and finally add the first term to the result sequence. This article provides Java code examples and explains the implementation logic of the code.

Aug 11, 2025 pm 07:12 PM

How to concatenate Strings in Java

The use of operators is suitable for simple string stitching, but is inefficient in loops; 2. The concat() method is used for small-scale direct stitching, returning new strings; 3. StringBuilder efficiently splices a large number of strings in a single thread, and is recommended for use in loops; 4. StringBuffer is a thread-safe StringBuilder, used in multi-threaded environments but has low performance; 5. String.join() is suitable for using delimiters to connect multiple strings or collection elements; 6. String.format() is used to format output; methods should be selected based on performance and readability to avoid using operators in loops.

Aug 11, 2025 pm 07:12 PM

Tutorial for generating a decreasing sequence algorithm for specifying sums

This tutorial aims to provide an algorithm that generates a decreasing sequence with a sum of 100 based on a given sequence length and first term value. By adjusting the sum and the sequence length and combining the decreasing proportion relationship, you can flexibly generate a sequence that meets specific requirements. The tutorial contains detailed code examples and explains key steps to help readers understand and apply the algorithm.

Aug 11, 2025 pm 07:06 PM

What is type casting in Java?

TypecastinginJavaistheprocessofconvertingavaluefromonedatatypetoanother,necessaryforcompatibilityinmixed-typeoperations.Therearetwomaintypes:1.ImplicitTypeCasting(WideningConversion)occursautomaticallywhenconvertingfromasmallertoalargerdatatype,sucha

Aug 11, 2025 pm 06:55 PM

java type conversion

How to use the Stream API to find the first element in Java?

Use the findFirst() method to get the first element in the JavaStream, which returns an Optional object. 1. Call stream().findFirst() to get the Optional result; 2. Use isPresent() to check whether there is an element, or use orElse() and ifPresent() to securely obtain the value; 3. You can combine intermediate operations such as filter() to find the first element that meets the conditions. This method returns the first element when encountering an ordered stream, is suitable for lists or arrays, and has short-circuit characteristics, efficient performance, and is the first choice for safety and standard.

Aug 11, 2025 pm 06:49 PM

Method to retrieve DatePicker value from a TableView selected cell

This document aims to solve the problem of obtaining the corresponding date value of the DatePicker control from the selected row of the TableView in JavaFX applications. By setting the data type of the date column to LocalDate, or performing date parsing when setting the value of DatePicker, you can effectively echo the selected date data in the TableView into the DatePicker control. This article will provide detailed implementation steps and sample code to help developers easily solve such problems.

Aug 11, 2025 pm 06:39 PM

What is a deadlock situation in Java and how can it be prevented?

Deadlock occurs in Java when two or more threads permanently block, waiting for each other's resources held by each other, forming a circular dependency. 1. Avoid nested locks, always acquire locks in a consistent order, and prevent loop waiting; 2. Use tryLock() with timeout to make the thread actively exit when it cannot acquire the lock; 3. Reduce the scope of the lock, and give priority to using lock-free structures such as ConcurrentHashMap and AtomicInteger; 4. Use tools such as jstack and VisualVM to detect deadlocks, and combine unit testing and static analysis tools to find potential problems; 5. Refactor the code to avoid holding multiple locks at the same time, such as using BlockingQueue for inter-thread communication rather than sharing state. By following this

Aug 11, 2025 pm 06:29 PM

java deadlock

How to use ExecutorService for managing threads in Java

UseExecutors.newFixedThreadPool(n),newCachedThreadPool(),newSingleThreadExecutor(),ornewScheduledThreadPool(n)tocreateanExecutorServiceformanagingthreadsefficiently.2.Submittasksviasubmit()usingRunnablefornoreturnvalueorCallabletoreturnaresult,obtain

Aug 11, 2025 pm 06:19 PM

Thread management