Document increment and decrement operators in SpEL

Closes gh-32136

framework-docs/modules/ROOT/pages/core/expressions/language-ref/operators.adoc

@@ -276,11 +276,19 @@ You can use the following operators on numbers, and standard operator precedence
 
 * addition (`+`)
 * subtraction (`-`)
+* increment (`{pp}`)
+* decrement (`--`)
 * multiplication (`*`)
 * division (`/`)
 * modulus (`%`)
 * exponential power (`^`)
 
+[NOTE]
+====
+The increment and decrement operators can be used with either prefix (`{pp}A`, `--A`) or
+postfix (`A{pp}`, `A--`) notation with variables or properties that can be written to.
+====
+
 The following example shows the mathematical operators in use:
 
 [tabs]
@@ -289,7 +297,11 @@ Java::
 +
 [source,java,indent=0,subs="verbatim,quotes",role="primary"]
 ----
+	Inventor inventor = new Inventor();
+	EvaluationContext context = SimpleEvaluationContext.forReadWriteDataBinding().build();
+
 	// -- Addition --
+
 	int two = parser.parseExpression("1 + 1").getValue(int.class);  // 2
 
 	// -- Subtraction --
@@ -298,6 +310,26 @@ Java::
 
 	double d = parser.parseExpression("1000.00 - 1e4").getValue(double.class);  // -9000
 
+	// -- Increment --
+
+	// The counter property in Inventor has an initial value of 0.
+
+	// evaluates to 2; counter is now 1
+	two = parser.parseExpression("counter++ + 2").getValue(context, inventor, int.class);
+
+	// evaluates to 5; counter is now 2
+	int five = parser.parseExpression("3 + ++counter").getValue(context, inventor, int.class);
+
+	// -- Decrement --
+
+	// The counter property in Inventor has a value of 2.
+
+	// evaluates to 6; counter is now 1
+	int six = parser.parseExpression("counter-- + 4").getValue(context, inventor, int.class);
+
+	// evaluates to 5; counter is now 0
+	five = parser.parseExpression("5 + --counter").getValue(context, inventor, int.class);
+
 	// -- Multiplication --
 
 	six = parser.parseExpression("-2 * -3").getValue(int.class);  // 6
@@ -329,6 +361,9 @@ Kotlin::
 +
 [source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
 ----
+	val inventor = Inventor()
+	val context = SimpleEvaluationContext.forReadWriteDataBinding().build()
+
 	// -- Addition --
 
 	var two = parser.parseExpression("1 + 1").getValue(Int::class.java)  // 2
@@ -339,6 +374,26 @@ Kotlin::
 
 	val d = parser.parseExpression("1000.00 - 1e4").getValue(Double::class.java)  // -9000
 
+	// -- Increment --
+
+	// The counter property in Inventor has an initial value of 0.
+
+	// evaluates to 2; counter is now 1
+	two = parser.parseExpression("counter++ + 2").getValue(context, inventor, Int::class.java)
+
+	// evaluates to 5; counter is now 2
+	var five = parser.parseExpression("3 + ++counter").getValue(context, inventor, Int::class.java)
+
+	// -- Decrement --
+
+	// The counter property in Inventor has a value of 2.
+
+	// evaluates to 6; counter is now 1
+	var six = parser.parseExpression("counter-- + 4").getValue(context, inventor, Int::class.java)
+
+	// evaluates to 5; counter is now 0
+	five = parser.parseExpression("5 + --counter").getValue(context, inventor, Int::class.java)
+
 	// -- Multiplication --
 
 	six = parser.parseExpression("-2 * -3").getValue(Int::class.java)  // 6

spring-expression/src/test/java/org/springframework/expression/spel/SpelDocumentationTests.java

@@ -306,43 +306,76 @@ void stringOperators() {
 
 	@Test
 	void mathematicalOperators() {
-		// Addition
+		Inventor inventor = new Inventor();
+		EvaluationContext context = SimpleEvaluationContext.forReadWriteDataBinding().build();
+
+		// -- Addition --
+
 		int two = parser.parseExpression("1 + 1").getValue(int.class);  // 2
 		assertThat(two).isEqualTo(2);
 
-		// Subtraction
+		// -- Subtraction --
+
 		int four = parser.parseExpression("1 - -3").getValue(int.class);  // 4
 		assertThat(four).isEqualTo(4);
 
 		double d = parser.parseExpression("1000.00 - 1e4").getValue(double.class);  // -9000
 		assertThat(d).isCloseTo(-9000.0d, within((double) 0));
 
-		// Multiplication
-		int six = parser.parseExpression("-2 * -3").getValue(int.class);  // 6
+		// -- Increment --
+
+		// The counter property in Inventor has an initial value of 0.
+
+		// evaluates to 2; counter is now 1
+		two = parser.parseExpression("counter++ + 2").getValue(context, inventor, int.class);
+		assertThat(two).isEqualTo(2);
+
+		// evaluates to 5; counter is now 2
+		int five = parser.parseExpression("3 + ++counter").getValue(context, inventor, int.class);
+		assertThat(five).isEqualTo(5);
+
+		// -- Decrement --
+
+		// The counter property in Inventor has a value of 2.
+
+		// evaluates to 6; counter is now 1
+		int six = parser.parseExpression("counter-- + 4").getValue(context, inventor, int.class);
+		assertThat(six).isEqualTo(6);
+
+		// evaluates to 5; counter is now 0
+		five = parser.parseExpression("5 + --counter").getValue(context, inventor, int.class);
+		assertThat(five).isEqualTo(5);
+
+		// -- Multiplication --
+
+		six = parser.parseExpression("-2 * -3").getValue(int.class);  // 6
 		assertThat(six).isEqualTo(6);
 
 		double twentyFour = parser.parseExpression("2.0 * 3e0 * 4").getValue(double.class);  // 24.0
 		assertThat(twentyFour).isCloseTo(24.0d, within((double) 0));
 
-		// Division
+		// -- Division --
+
 		int minusTwo = parser.parseExpression("6 / -3").getValue(int.class);  // -2
 		assertThat(minusTwo).isEqualTo(-2);
 
 		double one = parser.parseExpression("8.0 / 4e0 / 2").getValue(double.class);  // 1.0
 		assertThat(one).isCloseTo(1.0d, within((double) 0));
 
-		// Modulus
+		// -- Modulus --
+
 		int three = parser.parseExpression("7 % 4").getValue(int.class);  // 3
 		assertThat(three).isEqualTo(3);
 
 		int oneInt = parser.parseExpression("8 / 5 % 2").getValue(int.class);  // 1
 		assertThat(oneInt).isEqualTo(1);
 
-		// Exponential power
+		// -- Exponential power --
+
 		int maxInt = parser.parseExpression("(2^31) - 1").getValue(int.class);  // Integer.MAX_VALUE
 		assertThat(maxInt).isEqualTo(Integer.MAX_VALUE);
 
-		// Operator precedence
+		// -- Operator precedence --
 
 		int minusTwentyOne = parser.parseExpression("1+2-3*8").getValue(int.class);  // -21
 		assertThat(minusTwentyOne).isEqualTo(-21);