Check if all objects have the property value of all other objects
From the question and the comment I'd argue that your object model needs refactoring. There should be an Action object (you might come up with a better name...) tat contains the date and both of the processes Inflate and Deflate (not having a date themselves).

However...

This is how I would approach this by avoiding to iterate processAmounts excessively

public void fixMissingProcesses(){
    Map&lt;String,Map&lt;Date,ProcessAmount&gt;&gt; processesPerName = separateProcessesByName();        
    List&lt;String&gt; processNames = new ArrayList&lt;&gt;(processesPerName.keySet());
    for(int i=1;i&lt;processNames.length();i++)
      for(int j=0;j&lt;i;j++)
         addMissingProcesses(processNames.get(i),processNames.get(j), processesPerName);
}    

private void separateProcessesByName(){
    Map&lt;String,Map&lt;Date,ProcessAmount&gt;&gt; processesPerName = new HasMap&lt;&gt;();        
    for (ProcessAmount processAmount : processAmounts) {
      if(null!=processAmount.getProcessName()){
         Map&lt;Date,ProcessAmount&gt; processesPerDate=  processesPerName.getOrDefault(processAmount.getProcessName(),new HashMap&lt;&gt;());
         processesPerDate.put(processAmount.getDate(),processAmount);
         processesPerName.put(processAmount.getProcessName(),processesPerDate)
      }
    }
    return processesPerName;
}    


private void addMissingProcesses(String sourceProcessName, String targetProcessName, Map&lt;String,Map&lt;Date,ProcessAmount&gt;&gt; processesPerName);
    for(Date checkDate: processesPerName.get(sourceProcessName).keySet()){
       if(!processesPerName.get(targetProcessName).containsKey(checkDate)){
         processAmounts.add(new  ProcessAmount(checkDate, 0, targetProcessName)
       }
    }
}