HashCodeTest

hackfengJam · hackfengJam · commit 70955f27ab3b · 2019-03-22T00:02:33.000+08:00
diff --git a/Hash/src/hashcode_test/HashCodeTest.java b/Hash/src/hashcode_test/HashCodeTest.java
@@ -0,0 +1,30 @@
+package hashcode_test;
+
+import java.util.HashMap;
+import java.util.HashSet;
+
+public class HashCodeTest {
+    public static void main(String[] args) {
+        int a = 42;
+        System.out.println(((Integer) a).hashCode());
+        int b = -42;
+        System.out.println(((Integer) b).hashCode());
+
+        double c = 3.1415926;
+        System.out.println(((Double) c).hashCode());
+
+        String d = "hackfun";
+        System.out.println(d.hashCode());
+
+        Student student = new Student(3, 2, "Hackfun", "jiang");
+        System.out.println(student.hashCode());
+
+
+        HashSet<Student> set = new HashSet<>();
+        set.add(student);
+
+        HashMap<Student, Integer> scores = new HashMap<>();
+        scores.put(student, 100);
+    }
+}
+
diff --git a/Hash/src/hashcode_test/Student.java b/Hash/src/hashcode_test/Student.java
@@ -0,0 +1,52 @@
+package hashcode_test;
+
+public class Student {
+
+    int grade;
+    int cls;
+    String firstName;
+    String lastName;
+
+    Student(int grade, int cls, String firstName, String lastName) {
+        this.grade = grade;
+        this.cls = cls;
+        this.firstName = firstName;
+        this.lastName = lastName;
+    }
+
+
+    public int hashCode() {
+
+        int B = 31;
+
+        int hash = 0;
+        hash = hash * B + grade;
+        hash = hash * B + cls;
+        hash = hash * B + firstName.toLowerCase().hashCode(); // 忽略大小写
+        hash = hash * B + lastName.toLowerCase().hashCode(); // 忽略大小写
+        // 可能产生溢出，但依然没有关系
+
+        return hash;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o)
+            return true;
+
+        if (o == null)
+            return false;
+
+
+        if (!(o instanceof Student) || getClass() != o.getClass())
+            return false;
+
+        Student another = (Student) o;
+
+        return this.grade == another.grade &&
+                this.cls == another.cls &&
+                this.firstName.toLowerCase().equals(another.firstName.toLowerCase()) &&
+                this.lastName.toLowerCase().equals(another.lastName.toLowerCase());
+    }
+
+}
