{"id":3007,"date":"2024-03-01T12:16:51","date_gmt":"2024-03-01T12:16:51","guid":{"rendered":"https:\/\/msgprogramator.sk\/?p=3007"},"modified":"2025-07-07T10:57:27","modified_gmt":"2025-07-07T10:57:27","slug":"java-strategy","status":"publish","type":"post","link":"https:\/\/msgprogramator.sk\/en\/java-strategy\/","title":{"rendered":"Java design pattern Strategy"},"content":{"rendered":"

Today we will look at the last Java<\/strong> design pattern<\/strong> from the category of behavioural patterns<\/strong> – Strategy. Java design patterns in this category deal with the interaction<\/strong> between objects and their responsibility<\/strong>.<\/p>\n

What is a Strategy design pattern?<\/h2>\n

Strategy <\/strong> is a design pattern that allows you to dynamically change the behaviour of a class or its algorithms as needed at runtime. For example, if we have a class that performs data validation, the structure of the data may not be known before execution, and the validation algorithm to be used is decided just before it is used. <\/p>\n

What problem does the Strategy design pattern solve?<\/h2>\n

The Strategy <\/strong> pattern addresses the problem of having the flexibility to change the way a certain functionality is implemented in a program at runtime. It allows you to define a family of algorithms or strategies, put each of them in a separate class, and ensure that their objects are interchangeable. <\/p>\n

The main goal is to provide the ability to dynamically change the behaviour of the object according to the chosen strategy. A context object is used to switch strategies, which has a reference to the strategy object and can also call its methods.<\/p>\n

Example of a Strategy implementation in Java<\/h2>\n

This code demonstrates the use of the Strategy <\/strong> design pattern in the context of a hockey coach and his ability to switch between offensive and defensive strategies based on the current state of the game.<\/p>\n

GameStrategy.java<\/u><\/strong><\/p>\n

package designpatterns;\n\npublic interface HernaStrategia {\n    void vykonat();\n}<\/code><\/pre>\n
GameStrategy<\/strong> is an interface that defines how to implement a strategy. It contains a single execute()<\/em> method that defines how the strategy is to be executed. <\/p>\n
OffensiveStrategy.java, DefensiveStrategy.java<\/u><\/strong><\/p>\n
package designpatterns;\n\npublic class UtocnaStrategia implements HernaStrategia {\n    @Override\n    public void vykonat() {\n        System.out.println("T\u00edm hr\u00e1 v \u00fato\u010dnej form\u00e1cii.");\n    }\n}\n\npublic class ObrannaStrategia implements HernaStrategia {\n    @Override\n    public void vykonat() {\n        System.out.println("T\u00edm prech\u00e1dza do obrannej form\u00e1cie.");\n    }\n}<\/code><\/pre>\n
OffensiveStrategy<\/strong> and DefensiveStrategy<\/strong> are concrete implementations of the GameStrategy<\/strong> interface. Each of these classes implements the execute()<\/em> method to execute a specific strategy – offensive or defensive. <\/p>\n
Coach.java<\/u><\/strong><\/p>\n
package designpatterns;\n\n\/\/ Kontext\npublic class Coach {\n    private HernaStrategia hernaStrategia;\n\n    public void zmenitStrategiu(HernaStrategia novaStrategia) {\n        this.hernaStrategia = novaStrategia;\n    }\n\n    public void vykonatStrategiu() {\n        hernaStrategia.vykonat();\n    }\n}<\/code><\/pre>\n
A coach is a context that uses a strategy. It has a GameStrategy attribute that holds the current strategy. The changeStrategy()<\/em> method is used to change the current strategy and the executeStrategy()<\/em> method executes it.<\/p>\n
Main.java<\/u><\/strong><\/p>\n
import designpatterns.Coach;\nimport designpatterns.HernaStrategia;\nimport designpatterns.ObrannaStrategia;\nimport designpatterns.UtocnaStrategia;\n\npublic class Main {\n    public static void main(String[] args) {\n        Coach coach = new Coach();\n        HernaStrategia utocnaStrategia = new UtocnaStrategia();\n        HernaStrategia obrannaStrategia = new ObrannaStrategia();\n\n        System.out.println("Za\u010dala sa hra.");\n\n        \/\/ Coach vyber\u00e1 strat\u00e9giu pod\u013ea priebehu hry\n        \/\/ Za\u010d\u00edname s \u00fato\u010dnou strat\u00e9giou\n        coach.zmenitStrategiu(utocnaStrategia);\n        coach.vykonatStrategiu();\n\n        System.out.println("T\u00edm striela g\u00f3l a vedie.");\n\n        \/\/ Ak t\u00edm vyhr\u00e1va, zmen\u00edme na obrann\u00fa strat\u00e9giu\n        \/\/ (simulujeme, \u017ee sa t\u00edm dost\u00e1va do obrannej f\u00e1zy, ke\u010f vedie v z\u00e1pase)\n        coach.zmenitStrategiu(obrannaStrategia);\n        coach.vykonatStrategiu();\n\n        System.out.println("S\u00faper striela g\u00f3l a vyrovn\u00e1va.");\n\n        \/\/ Ak t\u00edm prehr\u00e1va, m\u00f4\u017eeme sa op\u00e4\u0165 vr\u00e1ti\u0165 k \u00fato\u010dnej strat\u00e9gii\n        \/\/ (simulujeme, \u017ee t\u00edm znova prech\u00e1dza do \u00fato\u010dnej f\u00e1zy, ke\u010f prehr\u00e1va)\n        coach.zmenitStrategiu(utocnaStrategia);\n        coach.vykonatStrategiu();\n    }\n}<\/code><\/pre>\n
The Main <\/strong> class creates a Coach <\/strong> instance and two strategy instances – offensive and defensive. This is followed by a simulation of the match, where the strategies change as the match progresses. <\/p>\n
The output of this example is:<\/p>\n
\"Output
The output of the Strategy design pattern example.<\/figcaption><\/figure>\n
Conclusion<\/h2>\n
The Strategy <\/strong> pattern is often used when we need to dynamically change the behaviour of a class or its strategies on the fly. <\/p>\n
We have prepared the files with the above example as code that you can run directly in Java. You can download the Java Strategy<\/strong> code here<\/a>.<\/p>\n
If you’re looking for a job and you’re a Java developer<\/a>, check out our employee benefits<\/a> and respond to our job offers<\/a>!<\/p>\n","protected":false},"excerpt":{"rendered":"
What is the Java Strategy design pattern and what is it for? Read our new article and download the sample code.<\/p>\n","protected":false},"author":14,"featured_media":2833,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[57],"tags":[],"class_list":["post-3007","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-java"],"acf":[],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t