public void setPrincipalId(String principalId) {
        this.principalId = principalId;
    }
<p>
The unique identifier of the principal assigned to the application.
</p>

@param principalId
       The unique identifier of the principal assigned to the application.
aws-java-sdk-ssoadmin/src/main/java/com/amazonaws/services/ssoadmin/model/ApplicationAssignment.java