feat: implement identifier-based equals/hashCode for PromptReference (#514)

Ensure PromptReference equality is based solely on identifier and type fields, ignoring other fields like title

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

mcp/src/main/java/io/modelcontextprotocol/spec/McpSchema.java

@@ -2351,6 +2351,22 @@ public final class McpSchema {
 		public String identifier() {
 			return name();
 		}
+
+		@Override
+		public boolean equals(Object obj) {
+			if (this == obj)
+				return true;
+			if (obj == null || getClass() != obj.getClass())
+				return false;
+			PromptReference that = (PromptReference) obj;
+			return java.util.Objects.equals(identifier(), that.identifier())
+					&& java.util.Objects.equals(type(), that.type());
+		}
+
+		@Override
+		public int hashCode() {
+			return java.util.Objects.hash(identifier(), type());
+		}
 	}
 
 	/**

mcp/src/test/java/io/modelcontextprotocol/spec/PromptReferenceEqualsTest.java

@@ -0,0 +1,87 @@
+/*
+* Copyright 2025 - 2025 the original author or authors.
+*/
+
+package io.modelcontextprotocol.spec;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Test class to verify the equals method implementation for PromptReference.
+ */
+class PromptReferenceEqualsTest {
+
+	@Test
+	void testEqualsWithSameIdentifierAndType() {
+		McpSchema.PromptReference ref1 = new McpSchema.PromptReference("ref/prompt", "test-prompt", "Test Title");
+		McpSchema.PromptReference ref2 = new McpSchema.PromptReference("ref/prompt", "test-prompt", "Different Title");
+
+		assertTrue(ref1.equals(ref2), "PromptReferences with same identifier and type should be equal");
+		assertEquals(ref1.hashCode(), ref2.hashCode(), "Equal objects should have same hash code");
+	}
+
+	@Test
+	void testEqualsWithDifferentIdentifier() {
+		McpSchema.PromptReference ref1 = new McpSchema.PromptReference("ref/prompt", "test-prompt-1", "Test Title");
+		McpSchema.PromptReference ref2 = new McpSchema.PromptReference("ref/prompt", "test-prompt-2", "Test Title");
+
+		assertFalse(ref1.equals(ref2), "PromptReferences with different identifiers should not be equal");
+	}
+
+	@Test
+	void testEqualsWithDifferentType() {
+		McpSchema.PromptReference ref1 = new McpSchema.PromptReference("ref/prompt", "test-prompt", "Test Title");
+		McpSchema.PromptReference ref2 = new McpSchema.PromptReference("ref/other", "test-prompt", "Test Title");
+
+		assertFalse(ref1.equals(ref2), "PromptReferences with different types should not be equal");
+	}
+
+	@Test
+	void testEqualsWithNull() {
+		McpSchema.PromptReference ref1 = new McpSchema.PromptReference("ref/prompt", "test-prompt", "Test Title");
+
+		assertFalse(ref1.equals(null), "PromptReference should not be equal to null");
+	}
+
+	@Test
+	void testEqualsWithDifferentClass() {
+		McpSchema.PromptReference ref1 = new McpSchema.PromptReference("ref/prompt", "test-prompt", "Test Title");
+		String other = "not a PromptReference";
+
+		assertFalse(ref1.equals(other), "PromptReference should not be equal to different class");
+	}
+
+	@Test
+	void testEqualsWithSameInstance() {
+		McpSchema.PromptReference ref1 = new McpSchema.PromptReference("ref/prompt", "test-prompt", "Test Title");
+
+		assertTrue(ref1.equals(ref1), "PromptReference should be equal to itself");
+	}
+
+	@Test
+	void testEqualsIgnoresTitle() {
+		McpSchema.PromptReference ref1 = new McpSchema.PromptReference("ref/prompt", "test-prompt", "Title 1");
+		McpSchema.PromptReference ref2 = new McpSchema.PromptReference("ref/prompt", "test-prompt", "Title 2");
+		McpSchema.PromptReference ref3 = new McpSchema.PromptReference("ref/prompt", "test-prompt", null);
+
+		assertTrue(ref1.equals(ref2), "PromptReferences should be equal regardless of title");
+		assertTrue(ref1.equals(ref3), "PromptReferences should be equal even when one has null title");
+		assertTrue(ref2.equals(ref3), "PromptReferences should be equal even when one has null title");
+	}
+
+	@Test
+	void testHashCodeConsistency() {
+		McpSchema.PromptReference ref1 = new McpSchema.PromptReference("ref/prompt", "test-prompt", "Test Title");
+		McpSchema.PromptReference ref2 = new McpSchema.PromptReference("ref/prompt", "test-prompt", "Different Title");
+
+		assertEquals(ref1.hashCode(), ref2.hashCode(), "Objects that are equal should have the same hash code");
+
+		// Call hashCode multiple times to ensure consistency
+		int hashCode1 = ref1.hashCode();
+		int hashCode2 = ref1.hashCode();
+		assertEquals(hashCode1, hashCode2, "Hash code should be consistent across multiple calls");
+	}
+
+}