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site</a></li></ul></li></ul></div></div><main id="page-content"><div id="site-toc--side" class="site-toc"><header class="site-toc__title">Contents</header><ul class="section-nav"><li class="toc-entry nav-item"><a class="nav-link" href="#instance-methods">Instance methods</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#operators">Operators</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#getters-and-setters">Getters and setters</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#abstract-methods">Abstract methods</a></li></ul></div><article><div class="content"><nav id="subnav"><ul><li class="previous"><a href="/language/constructors">&lang;  Constructors</a></li><li class="next"><a href="/language/extend">Extend a class  &rang;</a></li></ul></nav><div id="site-content-title"><h1>Methods</h1></div><div id="site-toc--inline" class="site-toc"><header class="site-toc__title">Contents</header><ul class="section-nav"><li class="toc-entry"><a href="#instance-methods">Instance methods</a></li><li class="toc-entry"><a href="#operators">Operators</a></li><li class="toc-entry"><a href="#getters-and-setters">Getters and setters</a></li><li class="toc-entry"><a href="#abstract-methods">Abstract methods</a></li></ul></div> <?code-excerpt replace="/ *\/\/\s+ignore_for_file:[^\n]+\n//g; /(^|\n) *\/\/\s+ignore:[^\n]+\n/$1/g; /(\n[^\n]+) *\/\/\s+ignore:[^\n]+\n/$1\n/g"?> <p>Methods are functions that provide behavior for an object.</p><div class="header-wrapper"><h2 id="instance-methods">Instance methods</h2><a class="heading-link" href="#instance-methods" aria-label="Link to 'Instance methods' section">#</a></div><p>Instance methods on objects can access instance variables and <code>this</code>. The <code>distanceTo()</code> method in the following sample is an example of an instance method:</p> <?code-excerpt "misc/lib/language_tour/classes/point.dart (class-with-distance-to)" plaster="none"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">import</span><span style="color:#11796D"> 'dart:math'</span><span style="color:#222222">;</span></span> <span class="line"></span> <span class="line"><span style="color:#D43324">class</span><span style="color:#0468D7"> Point</span><span style="color:#222222"> {</span></span> <span class="line"><span style="color:#D43324"> final</span><span style="color:#0468D7"> double</span><span style="color:#222222"> x;</span></span> <span class="line"><span style="color:#D43324"> final</span><span style="color:#0468D7"> double</span><span style="color:#222222"> y;</span></span> <span class="line"></span> <span class="line"><span style="color:#6E6E70"> // Sets the x and y instance variables</span></span> <span class="line"><span style="color:#6E6E70"> // before the constructor body runs.</span></span> <span class="line"><span style="color:#0468D7"> Point</span><span style="color:#222222">(</span><span style="color:#D43324">this</span><span style="color:#222222">.x, </span><span style="color:#D43324">this</span><span style="color:#222222">.y);</span></span> <span class="line"></span> <span class="line"><span style="color:#0468D7"> double</span><span style="color:#6200EE"> distanceTo</span><span style="color:#222222">(</span><span style="color:#0468D7">Point</span><span style="color:#222222"> other) {</span></span> <span class="line"><span style="color:#D43324"> var</span><span style="color:#222222"> dx = x - other.x;</span></span> <span class="line"><span style="color:#D43324"> var</span><span style="color:#222222"> dy = y - other.y;</span></span> <span class="line"><span style="color:#D43324"> return</span><span style="color:#6200EE"> sqrt</span><span style="color:#222222">(dx * dx + dy * dy);</span></span> <span class="line"><span style="color:#222222"> }</span></span> <span class="line"><span style="color:#222222">}</span></span></code></pre></div></div><div class="header-wrapper"><h2 id="operators">Operators</h2><a class="heading-link" href="#operators" aria-label="Link to 'Operators' section">#</a></div><p>Most operators are instance methods with special names. Dart allows you to define operators with the following names:</p><div class="table-wrapper"><table class="table"><thead><tr><th></th><th></th><th></th><th></th><th></th><th></th></tr></thead><tbody><tr><td><code><</code></td><td><code>></code></td><td><code><=</code></td><td><code>>=</code></td><td><code>==</code></td><td><code>~</code></td></tr><tr><td><code>-</code></td><td><code>+</code></td><td><code>/</code></td><td><code>~/</code></td><td><code>*</code></td><td><code>%</code></td></tr><tr><td><code>|</code></td><td><code>藛</code></td><td><code>&</code></td><td><code><<</code></td><td><code>>>></code></td><td><code>>></code></td></tr><tr><td><code>[]=</code></td><td><code>[]</code></td><td></td><td></td><td></td><td></td></tr></tbody></table></div><aside class="alert alert-info"><div class="alert-header"><i class="material-symbols" aria-hidden="true">info</i> <span>Note</span></div><div class="alert-content"><p>You may have noticed that some <a href="/language/operators">operators</a>, like <code>!=</code>, aren't in the list of names. These operators aren't instance methods. Their behavior is built in to Dart.</p></div></aside><p>To declare an operator, use the built-in identifier <code>operator</code> then the operator you are defining. The following example defines vector addition (<code>+</code>), subtraction (<code>-</code>), and equality (<code>==</code>):</p> <?code-excerpt "misc/lib/language_tour/classes/vector.dart"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">class</span><span style="color:#0468D7"> Vector</span><span style="color:#222222"> {</span></span> <span class="line"><span style="color:#D43324"> final</span><span style="color:#0468D7"> int</span><span style="color:#222222"> x, y;</span></span> <span class="line"></span> <span class="line"><span style="color:#0468D7"> Vector</span><span style="color:#222222">(</span><span style="color:#D43324">this</span><span style="color:#222222">.x, </span><span style="color:#D43324">this</span><span style="color:#222222">.y);</span></span> <span class="line"></span> <span class="line"><span style="color:#0468D7"> Vector</span><span style="color:#D43324"> operator</span><span style="color:#222222"> +(</span><span style="color:#0468D7">Vector</span><span style="color:#222222"> v) => </span><span style="color:#0468D7">Vector</span><span style="color:#222222">(x + v.x, y + v.y);</span></span> <span class="line"><span style="color:#0468D7"> Vector</span><span style="color:#D43324"> operator</span><span style="color:#222222"> -(</span><span style="color:#0468D7">Vector</span><span style="color:#222222"> v) => </span><span style="color:#0468D7">Vector</span><span style="color:#222222">(x - v.x, y - v.y);</span></span> <span class="line"></span> <span class="line"><span style="color:#D43324"> @override</span></span> <span class="line"><span style="color:#0468D7"> bool</span><span style="color:#D43324"> operator</span><span style="color:#222222"> ==(</span><span style="color:#0468D7">Object</span><span style="color:#222222"> other) =></span></span> <span class="line"><span style="color:#222222"> other is </span><span style="color:#0468D7">Vector</span><span style="color:#222222"> && x == other.x && y == other.y;</span></span> <span class="line"></span> <span class="line"><span style="color:#D43324"> @override</span></span> <span class="line"><span style="color:#0468D7"> int</span><span style="color:#D43324"> get</span><span style="color:#222222"> hashCode => </span><span style="color:#0468D7">Object</span><span style="color:#222222">.</span><span style="color:#6200EE">hash</span><span style="color:#222222">(x, y);</span></span> <span class="line"><span style="color:#222222">}</span></span> <span class="line"></span> <span class="line"><span style="color:#D43324">void</span><span style="color:#6200EE"> main</span><span style="color:#222222">() {</span></span> <span class="line"><span style="color:#D43324"> final</span><span style="color:#222222"> v = </span><span style="color:#0468D7">Vector</span><span style="color:#222222">(</span><span style="color:#11796D">2</span><span style="color:#222222">, </span><span style="color:#11796D">3</span><span style="color:#222222">);</span></span> <span class="line"><span style="color:#D43324"> final</span><span style="color:#222222"> w = </span><span style="color:#0468D7">Vector</span><span style="color:#222222">(</span><span style="color:#11796D">2</span><span style="color:#222222">, </span><span style="color:#11796D">2</span><span style="color:#222222">);</span></span> <span class="line"></span> <span class="line"><span style="color:#D43324"> assert</span><span style="color:#222222">(v + w == </span><span style="color:#0468D7">Vector</span><span style="color:#222222">(</span><span style="color:#11796D">4</span><span style="color:#222222">, </span><span style="color:#11796D">5</span><span style="color:#222222">));</span></span> <span class="line"><span style="color:#D43324"> assert</span><span style="color:#222222">(v - w == </span><span style="color:#0468D7">Vector</span><span style="color:#222222">(</span><span style="color:#11796D">0</span><span style="color:#222222">, </span><span style="color:#11796D">1</span><span style="color:#222222">));</span></span> <span class="line"><span style="color:#222222">}</span></span></code></pre></div></div><div class="header-wrapper"><h2 id="getters-and-setters">Getters and setters</h2><a class="heading-link" href="#getters-and-setters" aria-label="Link to 'Getters and setters' section">#</a></div><p>Getters and setters are special methods that provide read and write access to an object's properties. Recall that each instance variable has an implicit getter, plus a setter if appropriate. You can create additional properties by implementing getters and setters, using the <code>get</code> and <code>set</code> keywords:</p> <?code-excerpt "misc/lib/language_tour/classes/rectangle.dart"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">class</span><span style="color:#0468D7"> Rectangle</span><span style="color:#222222"> {</span></span> <span class="line"><span style="color:#0468D7"> double</span><span style="color:#222222"> left, top, width, height;</span></span> <span class="line"></span> <span class="line"><span style="color:#0468D7"> Rectangle</span><span style="color:#222222">(</span><span style="color:#D43324">this</span><span style="color:#222222">.left, </span><span style="color:#D43324">this</span><span style="color:#222222">.top, </span><span style="color:#D43324">this</span><span style="color:#222222">.width, </span><span style="color:#D43324">this</span><span style="color:#222222">.height);</span></span> <span class="line"></span> <span class="line"><span style="color:#6E6E70"> // Define two calculated properties: right and bottom.</span></span> <span class="line"><span style="color:#0468D7"> double</span><span style="color:#D43324"> get</span><span style="color:#222222"> right => left + width;</span></span> <span class="line"><span style="color:#D43324"> set</span><span style="color:#6200EE"> right</span><span style="color:#222222">(</span><span style="color:#0468D7">double</span><span style="color:#222222"> value) => left = value - width;</span></span> <span class="line"><span style="color:#0468D7"> double</span><span style="color:#D43324"> get</span><span style="color:#222222"> bottom => top + height;</span></span> <span class="line"><span style="color:#D43324"> set</span><span style="color:#6200EE"> bottom</span><span style="color:#222222">(</span><span style="color:#0468D7">double</span><span style="color:#222222"> value) => top = value - height;</span></span> <span class="line"><span style="color:#222222">}</span></span> <span class="line"></span> <span class="line"><span style="color:#D43324">void</span><span style="color:#6200EE"> main</span><span style="color:#222222">() {</span></span> <span class="line"><span style="color:#D43324"> var</span><span style="color:#222222"> rect = </span><span style="color:#0468D7">Rectangle</span><span style="color:#222222">(</span><span style="color:#11796D">3</span><span style="color:#222222">, </span><span style="color:#11796D">4</span><span style="color:#222222">, </span><span style="color:#11796D">20</span><span style="color:#222222">, </span><span style="color:#11796D">15</span><span style="color:#222222">);</span></span> <span class="line"><span style="color:#D43324"> assert</span><span style="color:#222222">(rect.left == </span><span style="color:#11796D">3</span><span style="color:#222222">);</span></span> <span class="line"><span style="color:#222222"> rect.right = </span><span style="color:#11796D">12</span><span style="color:#222222">;</span></span> <span class="line"><span style="color:#D43324"> assert</span><span style="color:#222222">(rect.left == -</span><span style="color:#11796D">8</span><span style="color:#222222">);</span></span> <span class="line"><span style="color:#222222">}</span></span></code></pre></div></div><p>With getters and setters, you can start with instance variables, later wrapping them with methods, all without changing client code.</p><aside class="alert alert-info"><div class="alert-header"><i class="material-symbols" aria-hidden="true">info</i> <span>Note</span></div><div class="alert-content"><p>Operators such as increment (++) work in the expected way, whether or not a getter is explicitly defined. To avoid any unexpected side effects, the operator calls the getter exactly once, saving its value in a temporary variable.</p></div></aside><div class="header-wrapper"><h2 id="abstract-methods">Abstract methods</h2><a class="heading-link" href="#abstract-methods" aria-label="Link to 'Abstract methods' section">#</a></div><p>Instance, getter, and setter methods can be abstract, defining an interface but leaving its implementation up to other classes. Abstract methods can only exist in <a href="/language/class-modifiers#abstract">abstract classes</a> or <a href="/language/mixins">mixins</a>.</p><p>To make a method abstract, use a semicolon (<code>;</code>) instead of a method body:</p> <?code-excerpt "misc/lib/language_tour/classes/doer.dart"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">abstract</span><span style="color:#D43324"> class</span><span style="color:#0468D7"> Doer</span><span style="color:#222222"> {</span></span> <span class="line"><span style="color:#6E6E70"> // Define instance variables and methods...</span></span> <span class="line"></span> <span class="line"><span style="color:#D43324"> void</span><span style="color:#6200EE"> doSomething</span><span style="color:#222222">(); </span><span style="color:#6E6E70">// Define an abstract method.</span></span> <span class="line"><span style="color:#222222">}</span></span> <span class="line"></span> <span class="line"><span style="color:#D43324">class</span><span style="color:#0468D7"> EffectiveDoer</span><span style="color:#D43324"> extends</span><span style="color:#0468D7"> Doer</span><span style="color:#222222"> {</span></span> <span class="line"><span style="color:#D43324"> void</span><span style="color:#6200EE"> doSomething</span><span style="color:#222222">() {</span></span> <span class="line"><span style="color:#6E6E70"> // Provide an implementation, so the method is not abstract here...</span></span> <span class="line"><span style="color:#222222"> }</span></span> <span class="line"><span style="color:#222222">}</span></span></code></pre></div></div><nav id="subnav"><ul><li class="previous"><a href="/language/constructors">&lang;  Constructors</a></li><li class="next"><a href="/language/extend">Extend a class  &rang;</a></li></ul></nav><p id="page-github-links"><span>Unless stated otherwise, the documentation on this site reflects Dart 3.5.4. 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