How to use different types of keys in one map in Java?
Apr 19, 2025 pm 05:45 PM
How to use different types of keys in Java?
In Java programs, Map is a common data structure that stores key-value pairs. But sometimes different types of keys are needed in a Map, such as integers and strings. Using different types as keys directly will throw a type mismatch error. This article will explore how to store different types of keys in Java Map and solve related problems.
Let’s first look at an example and try to add different types of key-value pairs to a custom dictionary class MyDictionary :
public class MyDictionary<k v> implements DictionaryInterface<k v> {
private map<k v> map;
public MyDictionary() {
map = new HashMap();
}
public void add(K key, V value) {
map.put(key, value);
}
public V get(K key) {
return map.get(key);
}
}
public class Main {
public static void main(String[] args) {
MyDictionary<integer string> dictionary = new MyDictionary();
dictionary.add(1, "100");
dictionary.add("1", "full score"); // Compile error}
}</integer></k></k></k>
In the above code, the type parameter of MyDictionary is defined as<k v></k> , supports any type of keys and values. But when trying to add a string type key to MyDictionary<integer string></integer> When , the compiler will report an error because the key type does not match the definition.
The solution is to define the type of key and value as Object :
public static void main(String[] args) {
MyDictionary<object object> dictionary = new MyDictionary();
dictionary.add(1, 100);
dictionary.add("1", "full score"); // Compile passed}</object>
By modifying the type parameter of MyDictionary to<object object></object> , you can freely add different types of keys. But this method requires type conversion when used, because Object type may cause a runtime type error.
In short, using Object as the type of key and value can store different types of keys in Java Map, but type conversions need to be handled with caution to avoid runtime errors. A better approach is to choose the right key type according to actual needs, or consider using more advanced data structures, such as custom classes as keys to encapsulate different types of data.
The above is the detailed content of How to use different types of keys in one map in Java?. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undress AI Tool
Undress images for free
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
The popularity of the currency circle has returned, why do smart people have begun to quietly increase their positions? Look at the trend from the on-chain data and grasp the next round of wealth password!
Jul 09, 2025 pm 08:30 PM
As the market conditions pick up, more and more smart investors have begun to quietly increase their positions in the currency circle. Many people are wondering what makes them take decisively when most people wait and see? This article will analyze current trends through on-chain data to help readers understand the logic of smart funds, so as to better grasp the next round of potential wealth growth opportunities.
What are the mainstream public chains of cryptocurrencies? The top ten rankings of cryptocurrency mainstream public chains in 2025
Jul 10, 2025 pm 08:21 PM
The pattern in the public chain field shows a trend of "one super, many strong ones, and a hundred flowers blooming". Ethereum is still leading with its ecological moat, while Solana, Avalanche and others are challenging performance. Meanwhile, Polkadot, Cosmos, which focuses on interoperability, and Chainlink, which is a critical infrastructure, form a future picture of multiple chains coexisting. For users and developers, choosing which platform is no longer a single choice, but requires a trade-off between performance, cost, security and ecological maturity based on specific needs.
Bitcoin breaks new highs, Dogecoin rebounds strongly, will Ethereum keep up with the pace
Jul 09, 2025 pm 08:24 PM
Recently, Bitcoin hit a new high, Dogecoin ushered in a strong rebound and the market was hot. Next, we will analyze the market drivers and technical aspects to determine whether Ethereum still has opportunities to follow the rise.
Cardano's smart contract evolution: The impact of Alonzo upgrades on 2025
Jul 10, 2025 pm 07:36 PM
Cardano's Alonzo hard fork upgrade has successfully transformed Cardano from a value transfer network to a fully functional smart contract platform by introducing the Plutus smart contract platform. 1. Plutus is based on Haskell language, with powerful functionality, enhanced security and predictable cost model; 2. After the upgrade, dApps deployment is accelerated, the developer community is expanded, and the DeFi and NFT ecosystems are developing rapidly; 3. Looking ahead to 2025, the Cardano ecosystem will be more mature and diverse. Combined with the improvement of scalability in the Basho era, the enhancement of cross-chain interoperability, the evolution of decentralized governance in the Voltaire era, and the promotion of mainstream adoption by enterprise-level applications, Cardano has
The flow of funds on the chain is exposed: What new tokens are being bet on by Clever Money?
Jul 16, 2025 am 10:15 AM
Ordinary investors can discover potential tokens by tracking "smart money", which are high-profit addresses, and paying attention to their trends can provide leading indicators. 1. Use tools such as Nansen and Arkham Intelligence to analyze the data on the chain to view the buying and holdings of smart money; 2. Use Dune Analytics to obtain community-created dashboards to monitor the flow of funds; 3. Follow platforms such as Lookonchain to obtain real-time intelligence. Recently, Cangming Money is planning to re-polize LRT track, DePIN project, modular ecosystem and RWA protocol. For example, a certain LRT protocol has obtained a large amount of early deposits, a certain DePIN project has been accumulated continuously, a certain game public chain has been supported by the industry treasury, and a certain RWA protocol has attracted institutions to enter.
Who issues stablecoins? What are the stablecoins?
Jul 09, 2025 pm 06:24 PM
Stablecoins are crypto assets that maintain price stability by anchoring fiat currencies such as the US dollar. They are mainly divided into three categories: fiat currency collateral, crypto asset collateral and algorithmic stablecoins. 1. USDT is issued by Tether and is the stablecoin with the largest market value and the highest liquidity. 2. USDC is released by the Centre alliance launched by Circle and Coinbase, and is known for its transparency and compliance. 3. DAI is generated by MakerDAO through over-collateralization of crypto assets and is the core currency in the DeFi field. 4. BUSD was launched in partnership with Paxos, and is regulated by the United States but has been discontinued. 5. TUSD achieves high transparency reserve verification through third-party escrow accounts. Users can use centralized exchanges such as Binance, Ouyi, and Huobi
What are the mainstream cryptocurrencies in the world? In-depth analysis of cryptocurrency in 2025 (including website)
Jul 10, 2025 pm 08:36 PM
At a time when the digital economy wave swept the world, cryptocurrencies have become the focus of attention from all walks of life with their unique decentralization and transparency. From the initial geek niche experiment to the current financial landscape with a market value of trillions, the evolution of cryptocurrencies is amazing. It not only brings innovations in underlying technologies, but also gives birth to countless innovative applications, which are profoundly affecting all aspects of finance, technology and even social governance.
Which chain does Dogecoin DOGE belong to? Does Dogecoin belong to the Binance Chain?
Jul 10, 2025 pm 08:39 PM
Recently, the discussion in the digital asset field has remained hot. Dogecoin DOGE, as one of the most popular focus, has become a question that many people have explored. Where does it "settling down"? What is the relationship with the current leading trading platform, Binance? To answer these questions, we need to conduct in-depth analysis from the two dimensions of the underlying technical logic of digital assets and the platform ecology, rather than just staying in appearance.
