124 lines
3.4 KiB
Plaintext
124 lines
3.4 KiB
Plaintext
[[variables]]
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=== Variables
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Variables in Painless must be declared and can be statically or <<dynamic-types,
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dynamically typed>>.
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[[variable-identifiers]]
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==== Variable Identifiers
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Specify variable identifiers using the following grammar. Variable identifiers
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must start with a letter or underscore. You cannot use <<keywords, keywords>> or
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<<types, types>> as identifiers.
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*Grammar:*
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[source,ANTLR4]
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----
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ID: [_a-zA-Z] [_a-zA-Z-0-9]*;
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----
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*Examples:*
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[source,Java]
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----
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_
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a
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Z
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id
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list
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list0
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MAP25
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_map25
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----
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[[variable-declaration]]
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==== Variable Declaration
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Variables must be declared before you use them. The format is `type-name
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identifier-name`. To declare multiple variables of the same type, specify a
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comma-separated list of identifier names. You can immediately assign a value to
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a variable when you declare it.
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*Grammar:*
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[source,ANTLR4]
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----
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type: ID ('[' ']')*;
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declaration : type ID (',' ID)*;
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----
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*Examples:*
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[source,Java]
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----
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int x; // Declare a variable with type int and id x
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List y; // Declare a variable with type List and id y
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int x, y, z; // Declare variables with type int and ids x, y, and z
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def[] d; // Declare the variable d with type def[]
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int i = 10; // Declare the int variable i and set it to the int literal 10
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----
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[[variable-assignment]]
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==== Variable Assignment
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Use the equals operator (`=`) to assign a value to a variable. The format is
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`identifier-name = value`. Any value expression can be assigned to any variable
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as long as the types match or the expression's type can be implicitly cast to
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the variable's type. An error occurs if the types do not match.
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*Grammar:*
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[source,ANTLR4]
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----
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assignment: ID '=' expression
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----
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*Examples:*
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Assigning a literal of the appropriate type directly to a declared variable.
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[source,Java]
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----
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int i; // Declare an int i
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i = 10; // Set the int i to the int literal 10
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----
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Immediately assigning a value when declaring a variable.
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[source,Java]
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----
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int i = 10; // Declare the int variable i and set it the int literal 1
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double j = 2.0; // Declare the double variable j and set it to the double
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// literal 2.0
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----
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Assigning a variable of one primitive type to another variable of the same
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type.
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[source,Java]
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----
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int i = 10; // Declare the int variable i and set it to the int literal 10
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int j = i; // Declare the int variable j and set it to the int variable i
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----
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Assigning a reference type to a new heap allocation with the `new` operator.
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[source,Java]
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----
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ArrayList l = new ArrayList(); // Declare an ArrayList variable l and set it
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// to a newly allocated ArrayList
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Map m = new HashMap(); // Declare a Map variable m and set it
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// to a newly allocated HashMap
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----
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Assigning a variable of one reference type to another variable of the same type.
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[source,Java]
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----
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List l = new ArrayList(); // Declare List variable l and set it a newly
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// allocated ArrayList
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List k = l; // Declare List variable k and set it to the
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// value of the List variable l
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List m; // Declare List variable m and set it the
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// default value null
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m = k; // Set the value of List variable m to the value
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// of List variable k
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----
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