(window.webpackJsonp=window.webpackJsonp||[]).push([[1548],{1955:function(s,t,a){"use strict";a.r(t);var n=a(31),e=Object(n.a)({},(function(){var s=this,t=s.$createElement,a=s._self._c||t;return a("ContentSlotsDistributor",{attrs:{"slot-key":s.$parent.slotKey}},[a("h1",{attrs:{id:"constructors"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#constructors"}},[s._v("#")]),s._v(" Constructors")]),s._v(" "),a("p",[s._v("While not required, constructors in Java are methods recognized by the compiler to instantiate specific values for the class which may be essential to the role of the object. This topic demonstrates proper usage of Java class constructors.")]),s._v(" "),a("h2",{attrs:{id:"default-constructor"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#default-constructor"}},[s._v("#")]),s._v(" Default Constructor")]),s._v(" "),a("p",[s._v('The "default" for constructors is that they do not have any arguments. In case you do not specify '),a("strong",[s._v("any")]),s._v(" constructor, the compiler will generate a default constructor for you."),a("br"),s._v("\nThis means the following two snippets are semantically equivalent:")]),s._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TestClass")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" test"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n")])])]),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TestClass")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" test"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TestClass")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n")])])]),a("p",[s._v("The visibility of the default constructor is the same as the visibility of the class. Thus a class defined package-privately has a package-private default constructor")]),s._v(" "),a("p",[s._v("However, if you have non-default constructor, the compiler will not generate a default constructor for you. So these are not equivalent:")]),s._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TestClass")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" test"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TestClass")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" arg"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n")])])]),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TestClass")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" test"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TestClass")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TestClass")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" arg"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n")])])]),a("p",[s._v("Beware that the generated constructor performs no non-standard initialization. This means all fields of your class will have their default value, unless they have an initializer.")]),s._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TestClass")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("private")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("String")]),s._v(" testData"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TestClass")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n        testData "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[s._v('"Test"')]),s._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("}")]),s._v("\n\n")])])]),a("p",[s._v("Constructors are called like this:")]),s._v(" "),a("div",{staticClass:"language-java extra-class"},[a("pre",{pre:!0,attrs:{class:"language-java"}},[a("code",[a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TestClass")]),s._v(" testClass "),a("span",{pre:!0,attrs:{class:"token operator"}},[s._v("=")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("new")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("TestClass")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(";")]),s._v("\n\n")])])]),a("h2",{attrs:{id:"call-parent-constructor"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#call-parent-constructor"}},[s._v("#")]),s._v(" Call parent constructor")]),s._v(" "),a("p",[s._v("Say you have a Parent class and a Child class. 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name and age are private,")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// making them invisible even to the child class.")]),s._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("class")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Child")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("extends")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Parent")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[s._v("public")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[s._v("Child")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v(")")]),s._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[s._v("{")]),s._v("\n        "),a("span",{pre:!0,attrs:{class:"token comment"}},[s._v("// compiler implicitly 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add "),a("code",[s._v("super")]),s._v(" in the Child constructor. 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