Design Authentication Manager LeetCode solution in Java

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class AuthenticationManager {
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  private int ttl;
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  private Map<String, Integer> map;
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  public AuthenticationManager(int timeToLive) {
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    this.ttl = timeToLive;
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    this.map = new HashMap<>();
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  }
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  public void generate(String tokenId, int currentTime) {
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    map.put(tokenId, currentTime + this.ttl);
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  }
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  public void renew(String tokenId, int currentTime) {
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    Integer expirationTime = this.map.getOrDefault(tokenId, null);
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    if (expirationTime == null || expirationTime <= currentTime) return;
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    generate(tokenId, currentTime);
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  }
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  public int countUnexpiredTokens(int currentTime) {
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    int count = 0;
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    for (Map.Entry<String, Integer> entry : this.map.entrySet())
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      if (entry.getValue() > currentTime) count++;
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    return count;
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  }
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}