Java:

Write a method named isHappyNumber that returns whether a given integer is "happy". An integer is "happy" if repeatedly summing the squares of its digits eventually leads to the number 1.

For example, 139 is happy because:

1² + 3² + 9² = 91

9² + 1² = 82

8² + 2² = 68

6² + 8² = 100

1² + 0² + 0² = 1

By contrast, 4 is not happy because:

4² = 16

1² + 6² = 37

3² + 7² = 58

5² + 8² = 89

8² + 9² = 145

1² + 4² + 5² = 42

4² + 2² = 20

2² + 0² = 4

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